Petri Dish Cookies

by Erin

As a scientist I can’t help but bring my work home. Microbiologists (and nerds) will love these petri dish cut out cookies with royal icing!

Petri Dish Cookies #scienceworks

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Many bakers make gorgeously decorated cookies that look too immaculate for a regular day person to accomplish. It’s this thing called royal icing, and it involves outlining, flooding and a bunch of little decorating tools. Sounds kind of daunting, which is why it took me so long to try for myself.

Ever since I saw a picture of these petri dish cookies, the lab nerd in me knew I had to join forces with my baking-side to make them. Since our lab just moved into a new facility and the ribbon cutting ceremony is scheduled to be today, I figured it was the perfect time to conquer my fear of royal icing. But I wasn’t about to do it without a little help.

Thanks to Michelle at Brown Eyed Baker and her wonderfully helpful tutorial on “How to Decorate Cookies with Royal Icing“, I bring to you these slightly unappetizing-looking, yet completely adorable (okay maybe I’m alone on that one) petri dish cookies!

Petri Dish Cookies #sciencecookies

Although there are a lot of steps, it’s pretty simple when you break it all down (and assuming you have all the necessary tools).

Things that will make life easier: 

I actually remade these for a holiday fundraiser at work which we called “Have yourself a Typhoid Mary Christmas” because the lab I work in now (2015-present 2020) works on Salmonella! We also made raw beef patties (pink rice crispy treats in patty shapes), chocolate covered cherry mice, expired “Christmofloxacin” jelly beans (ciprofloxacin is a drug used to treat), and lumps of gallstones (chocolate covered raisins in baggies).


Yield: Approximately 2 dozen
Nutrition facts: 200 calories 20 grams fat



  • 1 cup (2 sticks) unsalted butter, room temperature
  • 3/4 cup sugar
  • 1 egg, room temperature
  • 1 tsp vanilla extract
  • 2 cups all-purpose flour
  • 1 tsp baking powder
  • 1/4 tsp salt



  1. In a large bowl, cream the butter and sugar until light and fluffy. Beat in egg and vanilla until just combined. Slowly beat in flour, baking powder, and salt until it comes together into a dough.
  2. Shape dough into two discs, wrap in plastic wrap, and refrigerate for at least 2 hours. (Well wrapped, the dough can be refrigerated for up to 3 days or frozen for up to 2 months.)
  3. Center a rack in the oven and preheat the oven to 350 degrees. Line two baking sheets with parchment or silicone mats.
  4. Working with one packet of dough at a time, on a clean floured surface roll out the dough evenly to a thickness of about 1/8-1/4 inch. Cut out the cookies (I used a 2-1/2 inch diameter round cookie cutter). Pull away the excess dough, saving the scraps for rerolling, and carefully lift the rounds onto the baking sheets with a spatula, leaving about 1-1/2 inches between the cookies. After you’ve rolled and cut the second packet of dough, you can form the scraps into a disk, then chill, roll, cut and bake.
  5. Bake the cookies one sheet at a time for 8-10 minutes, rotating the sheet at the midpoint. The cookies should feel firm, but they should not color much. Remove the pan from the oven and let them rest for 1 minute before carefully lifting them onto a rack to cool to room temperature.
  6. Repeat with the remaining dough, cooling the baking sheets between batches. Allow cookies to cool completely before decorating.
  7. While the cookies cool make the icing: mix all ingredients on low speed for 7-10 minutes or until the icing loses its shine. Add more water by the teaspoon if it appears too stiff, or more powdered sugar if too thin. At this stage you want to be able to pipe it easily.
  8. Color the icing and then cover the container with a damp paper towel. It is key when working with royal icing not to allow it to dry out.
  9. Outline the cookies with the royal icing. Place some of the icing into a disposable pastry bag fitted with a #2 tip and coupler and outline the outside of the cookie. Keep the tip about 1/2-inch above the cookie while moving it allows the icing to lay on the cookie more easily. Make sure that the outline is pretty well set before moving on to flooding the cookies (generally by the time  you are done outlining the first ones are already dry).
  10. To the remaining icing, slowly start adding a few drops of water at a time, until the icing reaches an almost liquid consistency. The test here is to pick some icing up with a spoon and let it drizzle back into the bowl – the drizzle should disappear into the bowl within 10 seconds. Once you have achieved this, you are ready.
  11. Either fill a squeeze bottle with the thinned icing or transfer it to a disposable pastry bag with a 1/4-inch hole cut off the end. Now squeeze in the icing to almost completely fill the inside the cookie. Then take a toothpick and gently use it to distribute the icing to any empty spots. Sprinkle with white nonpareils**.
  12. Allow to dry completely before storing. The cookies will keep at room temperature in a tin for up to 1 week. Wrapped well, they can be frozen for up to 2 months.


*This color is extremely close to the YPD media we use to grow yeast in lab. And when I remade these I also used red for XLD and green for EBU plates with black sprinkles. ** Want that tri-streak effect? Save some of the icing as plain white and pipe it on top of the flooded icing.

Did You Make This Recipe?
I want to see! Tag me on Instagram at @TheSpiffyCookie and hashtag it #TheSpiffyCookie.

Source: Sugar Cookies from my Cut Out Sugar Cookies and Brown Eyed Baker, originally from Baking: From My Home to Yours by Dorie Greenspan, pages 146-147. Royal Icing and Tutorial from Brown Eyed Baker.

Post updated 10/9/20, photos above and below are the originals.

Did you make this recipe? I want to see!
Tag @THESPIFFYCOOKIE on Instagram and hashtag it #THESPIFFYCOOKIE

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Shannon September 5, 2011 - 3:51 pm

Too funny that you posted that bow picture. I just showed my boyfriend the picture and asked him if his school’s bow looked the same and it was the same building he has been telling me about! He is in pharmacy school. Love the cookies, I’m always nervous to work with royal icing too!

spiffycookie September 5, 2011 - 7:29 pm

Ha! Well how about that, what a small blogging world we live in.

Vicki @ WITK August 27, 2011 - 5:42 pm

These are very fun and nerdy, I love the pics! Sometimes you just have to embrace your inner nerd through other avenues than labwork! :)

spiffycookie August 27, 2011 - 6:08 pm

Oh yea let the nerdy flow!

kita August 27, 2011 - 4:51 pm

I have never decorated anything with royal icing because it does seem like such a task. These little cookies are adorable and I really need to kick this on my cooking bucket list! Thanks for the inspiration and links to check out.

spiffycookie August 27, 2011 - 6:08 pm

It was fun, I’m so glad I finally did it. You definitely should too!

Deb August 25, 2011 - 10:30 pm

Ingenious cookies! I very much enjoyed your post. Your instructions were informative yet concise. And I adored your “lab nerd” story. It was enjoyable!

Reem August 25, 2011 - 9:34 pm

These looks so cute… I bet they are delicious too. Great job.

San @ Obviously Cheddar August 25, 2011 - 8:14 pm

Erin, reading this post has inspired me to want to bake again. I went to school for Pastry and Baking @ Le Cordon Bleu here in Minnesota and sadly, I have lost touch with my baking skills because I have been mostly focusing on the culinary side. This was a great read with great instructions!

spiffycookie August 25, 2011 - 8:56 pm

Aw you can’t neglect your baking skills! Glad to be an inspiration.

Kelly August 25, 2011 - 7:51 pm

These cookies are so cute and look delicious, love the name! :)

Cassie (Bake Your Day) August 25, 2011 - 7:24 pm

Ummm these are the most perfectly round cookies I’ve ever seen in my life. I love this idea. I’m not such a patient baker so when it comes to batch after batch of cookies, I get to the point that my cookies are more like misshaped globs of dough rather than nicely shaped rounds. Great idea!

spiffycookie August 25, 2011 - 8:55 pm

Thanks! I did have a cookie cutter to thank for the round-ness. And I’m not patient if things start to fall apart or not work, but thankfully that didn’t happen this time around.

Michelle August 25, 2011 - 4:59 pm

these turned out perfectly!!!

Erin @ Dinners, Dishes and Desserts August 25, 2011 - 2:41 pm

Love the cookies! What a cute idea!
I have an award for you, if you want to stop by my site

spiffycookie August 25, 2011 - 2:46 pm

Wow thank you so much! I really need to get on with passing along awards I have received from you and others but I keep forgetting :-(

Lauren at Keep It Sweet August 25, 2011 - 12:39 pm

Ha, great idea! The cookies look terrific.

spiffycookie August 25, 2011 - 1:08 pm

Thanks I’m super excited about how they turned out. And they are a huge hit at work! Gotta love working with a bunch of nerds.

Food Snots August 25, 2011 - 12:19 pm

This is such a freakin cute idea!!

spiffycookie August 25, 2011 - 1:09 pm

I’m glad you think it’s cute and not gross-looking!

Steph@stephsbitebybite August 25, 2011 - 11:32 am

Great step by step instructions!! I am loving that yellow color!

spiffycookie August 25, 2011 - 1:09 pm

Thanks, Michelle has even better instructions with photos, check them out.

Miriam @ Overtime Cook August 25, 2011 - 8:54 am

Looks great! Very impressive for a first time. I can imagine that while eating those you have to try not to think of the nonpareils you have to try not to think of them as little colonies of bacteria or whatever!

Nice job, and very creative.


spiffycookie August 25, 2011 - 10:34 am

Hah yea, I work with yeast that looks awfully like that on a agarose plate! Thank you :-)

Bonnie Davis August 25, 2011 - 8:45 am

I’ll definitely be trying that. Thanks for the easy-to-follow directions! The cookies look delish.

spiffycookie August 25, 2011 - 8:49 am

Thanks! I really enjoyed making them.


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