Combine milk and flour in saucepan and whisk until combined. Set over medium-low heat and whisk constantly until mixture is thickened to a near paste-like consistency that wants to cling together.
Remove from heat and allow to cool completely, stirring occasionally to prevent a skin from forming. Set aside while you prepare your cookies.
Preheat your oven to 450F (235C) and line several baking sheets with parchment paper. Set aside.
In a large mixing bowl, combine sugar and butter and use an electric mixer to beat until well-combined.
Add egg and vanilla extract and beat again until pale yellow and well-combined.
With mixer on low-speed, gradually stir in buttermilk. Set aside.
In a separate, medium-sized bowl whisk together the flour, cocoa powder, baking soda, baking powder, and salt.
Gradually add the dry ingredients to the batter until completely combined.
Add very hot water (carefully) and stir until batter is well-combined and smooth. It will be thin like a cake batter. Use a spatula to scrape the sides and bottom of the bowl to ensure ingredients are well-combined.
Drop cookie batter by a heaping Tablespoon onto prepared baking sheets, spacing cookies at least 2” (5cm) apart.
Bake for 5-6 minutes in center rack of 450F (235C) preheated oven, then remove from oven and allow to cool completely before removing from baking sheet. As the cookies cool, prepare your filling.
Important note: The roux must be completely cooled before proceeding.
Place butter in a large mixing bowl (or the bowl of a stand mixer) and use an electric mixer to beat until smooth, light, and creamy.
While mixing on medium/low speed, add the flour mixture, a Tablespoon at a time, waiting until each spoonful is incorporated before adding the next.
Scrape sides and bottom of bowl and stir in salt and vanilla extract.
Gradually stir in powdered sugar until completely combined.
Pipe or spoon filling onto the bottom of one chocolate cookie and sandwich with another (about 1 ½ Tablespoon of filling per cookie). Enjoy!
Combine milk and flour in saucepan and whisk until combined. Set over medium-low heat and whisk constantly until mixture is thickened to a near paste-like consistency that wants to cling together.
Remove from heat and allow to cool completely, stirring occasionally to prevent a skin from forming. Set aside while you prepare your cookies.
Preheat your oven to 450F (235C) and line several baking sheets with parchment paper. Set aside.
In a large mixing bowl, combine sugar and butter and use an electric mixer to beat until well-combined.
Add egg and vanilla extract and beat again until pale yellow and well-combined.
With mixer on low-speed, gradually stir in buttermilk. Set aside.
In a separate, medium-sized bowl whisk together the flour, cocoa powder, baking soda, baking powder, and salt.
Gradually add the dry ingredients to the batter until completely combined.
Add very hot water (carefully) and stir until batter is well-combined and smooth. It will be thin like a cake batter. Use a spatula to scrape the sides and bottom of the bowl to ensure ingredients are well-combined.
Drop cookie batter by a heaping Tablespoon onto prepared baking sheets, spacing cookies at least 2” (5cm) apart.
Bake for 5-6 minutes in center rack of 450F (235C) preheated oven, then remove from oven and allow to cool completely before removing from baking sheet. As the cookies cool, prepare your filling.
Important note: The roux must be completely cooled before proceeding.
Place butter in a large mixing bowl (or the bowl of a stand mixer) and use an electric mixer to beat until smooth, light, and creamy.
While mixing on medium/low speed, add the flour mixture, a Tablespoon at a time, waiting until each spoonful is incorporated before adding the next.
Scrape sides and bottom of bowl and stir in salt and vanilla extract.
Gradually stir in powdered sugar until completely combined.
Pipe or spoon filling onto the bottom of one chocolate cookie and sandwich with another (about 1 ½ Tablespoon of filling per cookie). Enjoy!