They are kinda like grown-up Oreos.

Cookies
190 g flour
75 g cocoa, extra dark
2 tablespoons powdered espresso
1 teaspoon baking soda
¼ teaspoon baking powder
315 g sugar
142 g unsalted butter
1 large egg, room temperature

Filling
113 g unsalted butter, room temperature
95 g shortening
350 g powdered sugar
50 g cocoa powder, extra dark
1 tablespoon powdered espresso
1 tablespoon vanilla extract

Preheat oven to 375 degrees. Into a medium-size bowl, sift together flour, cocoa powder, baking soda, baking powder, and salt. Set aside.

In the bowl of an electric mixer fitted with the paddle attachment, cream sugar and butter until light and fluffy, about 2 minutes. Add egg; beat to combine. With mixer on low speed, gradually add the flour mixture; continue beating until dough is well combined.

Measure out 15 g size drops of dough and roll them into a ball.   Place them about 2 inches apart. Flatten them with a glass to about 1/8 inch thick.  Be gentle as you peel it off the glass.

Bake until cookies are firm, about 10 to 12 minutes, rotating baking sheets halfway through.  I also like to drop the cookie sheet on the counter so that they deflate and crack. Transfer baking sheets to wire racks to cool completely.

In the bowl of an electric mixer fitted with the paddle attachment, cream butter and shortening until well combined. With mixer on low speed, gradually add the powdered sugar, and cocoa. Continue beating until light and fluffy, about 2 minutes. Add the vanilla, and beat to combine. Set aside in a pastry bag at room temperature until ready to use. Pipe about a teaspoon on each and flatten with cookie on top to make a sandwich.