Whisk together flour, salt, and baking powder in a medium bowl; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar; mix until light and fluffy. With mixer running, add egg, brandy or milk, and vanilla; mix until well combined. With the mixer on low, slowly add reserved flour mixture. Mix until just combined.
Transfer half of dough to a work surface. In the bowl of your mixer add 1/8 tsp of food coloring (I used Wilton Violet). Mix until just evenly distributed, try not to overmix.
Place your white dough between two pieces of wax or parchment paper and roll into a rectangle as best you can. Repeat with the colored dough. Place on a baking sheet and put it in the refrigerator to chill for 30 minutes.
Remove the dough from the refrigerator and peel the paper off of one side of the colored dough. Lightly flour your work surface and flip the dough over onto it, then peel off the paper from the other side. Lightly brush the top of the colored dough with water.
Peel the paper off of one side of your white dough. Place it dough side down on top of the colored dough, trying to align the two rectangles of dough as well as possible. Then peel the paper from the other side. Try not to break your dough into pieces, but if you do just gently smoosh them back on.
Use a sharp knife to trim the edges of your rectangle so they are straight and even. Start to gently roll the dough. Continue until it is all rolled up. You might see some gaps if you look at the side of the dough. You don’t want those so gently roll the dough with two hands until the gaps disappear.
In a pan, empty your sprinkles or non pareils or whatever cookie decoration you like. Brush the dough with water, then gently roll in the toppings, pushing the toppings into the dough so they stick. Wrap with plastic wrap: Place in the refrigerator for one hour to firm up.
Preheat oven to 350 degrees. Remove dough from the fridge and trim the ends of the dough flat. Prepare two cookie sheets with parchment paper or silicone baking mats. Evenly slice the roll to about 1/4-inch thickness. Place on cookie sheet.
Bake until lightly golden, about ten minutes; do not allow to brown. Transfer to wire racks to cool.