These are ridiculously rich chocolate cookies with cream cheese frosting and crushed Oreos on top. They're basically what happens when you cross a brownie with a cookie and then pile frosting on it.
Preheat oven to 350F. Cream 3/4 cup butter, 1/3 cup granulated sugar, and 3/4 cup brown sugar until light and fluffy, about 3-4 minutes.
Beat in 1 egg and 1/2 Tbsp vanilla until smooth and creamy.
Add 1 1/2 cups flour, 1/2 cup black cocoa powder, crushed Oreos, 1 tsp baking soda, 1/2 tsp baking powder, and 1/4 tsp salt. Mix on low speed until just combined.
Portion dough using a 1/4 cup measuring cup onto baking sheets, spacing 6 cookies per sheet. Roll each portion into a ball and flatten into a thick disc.
Bake 12-15 minutes until tops are set and no longer glossy.
Cool on pan for 20 minutes before frosting.
While cookies cool, beat 2 Tbsp softened butter, 4 oz cream cheese, and 1 tsp vanilla until smooth. Add 2 cups powdered sugar one cup at a time, beating well. Add milk 1 tsp at a time if needed for piping consistency.
Transfer frosting to a gallon zip-top bag with one corner cut off. Pipe frosting in a spiral on each cookie and sprinkle crushed Oreos on top while frosting is soft.
Store in an airtight container on the counter for up to 3 days.
Notes
Cookies spread significantly, so flatten dough before baking and allow adequate space between portions.