01 -
Whip butter with both sugars to make it fluffy, about 3-5 minutes. Stir in egg. Add flour, cocoa powder, salt, and baking soda, mixing until it's all blended together.
02 -
Divide your dough into two parts. Roll each out between parchment paper to about 1/8 inch thickness. Let it chill for 30-40 minutes.
03 -
Use a cutter to make circles about 1 1/2 inches wide. Place the circles on lined pans, keeping them an inch apart. Bake in a 350°F oven for 12-14 minutes—look for them to firm up.
04 -
Beat butter until creamy. Slowly mix in powdered sugar, followed by milk, vanilla, and the salt, until it’s light and fluffy.
05 -
Spread or pipe some filling onto the flat side of one cookie, then press another cookie on top, flat sides touching.