Directions

1. In a medium saucepan over medium heat, add the half and half and 6 Tbsp of the sugar, stirring occasionally until it starts to simmer.
2. Meanwhile in a medium bowl, whisk the egg yolks until smooth. Add sugar and whisk to combine. Add cornstarch and whisk until combined and pale yellow (about 30 seconds).
3. Slowly stream half the simmering half and half mixture into the egg yolk mixture, whisking constantly. Add tempered egg mixture back into the saucepan while whisking constantly. Continue to stir until mixture is thickened and glossy (about 1 minute).
4. Pour dairy mixture into a bowl through a fine mesh strainer (to remove any lumps)**, using a spatula to help push it through.
5. Immediately whisk in butter and vanilla, then whisk in peanut butter until smooth. Cover with plastic wrap, pressing onto the surface, and place in fridge to cool (at least 4 hours).
6. Preheat oven to 350 degrees and grease a 9x9-inch square bundt pan* with non-stick spray, set aside.
7. In a small bowl, add all the filling/topping ingredients and cut in butter until it resembles coarse crumbs. Set aside.
8. In a medium bowl, whisk together the flour, cocoa powder, cinnamon, baking powder, baking soda, and salt. Set aside.
9. In a small bowl, mix the buttermilk and vanilla. Set aside.
10. In a large bowl with an electric mixer, beat together the butter and sugars until light and fluffy. Add the eggs and beat until just incorporated. Alternate adding in the flour mixture and buttermilk mixture, mixing just until combined.
11. Pour half the batter into prepared pan and spread evenly. Top with half of the filling/topping and pour remaining batter evenly on top. Sprinkle remaining filling on top, pressing lightly to make it stick.
12. Using the back of a spoon, gently press a shallow, channel or "ring" into the top layer of the cake batter, leaving a center island of batter intact.
13. Generously pipe the pastry cream (in a piping bag or a zip-top bag with the corner snipped) as a thick ring into the channel (you will likely have leftover pastry cream).
14. Bake for 45-55 minutes or until a toothpick inserted into the center of the cake comes out mostly clean with just a few crumbs (or an instant read thermometer reads 200F). Let cool 10 minutes before removing from pan to cool completely on a wire rack.
15. In a small bowl, whisk together powdered sugar, milk, and vanilla until smooth, adding more milk if necessary for desire consistency. Drizzle over cooled cake. Allow glaze to harden and serve.