Preheat oven to 350°F. Line baking sheets with parchment paper.
Whisk together flour, cocoa powder, baking soda, baking powder, and salt.
Beat butter, granulated sugar, and brown sugar until light and fluffy.
Add eggs, milk, and vanilla. Mix until combined.
Add dry ingredients and mix until the dough comes together and is smooth.
Scoop tablespoon-sized portions and roll into balls. Place on prepared baking sheets and press an indentation into each ball using the back of a teaspoon.Tip: Dip the back of the teaspoon in baking cocoa to prevent it from sticking to the cookie dough.
Bake for 7–9 minutes.
Immediately press the centers down again while the cookies are still warm. Cool completely.
Heat the heavy cream until hot. Pour over the chocolate chips and let stand for 2–3 minutes. Stir until smooth.
Spoon ganache into the center of each cooled cookie. Add sprinkles. Allow the filling to set before serving.
Video
Notes
The cookies are delicious on day one and soften a little after storage.Store in an airtight container at room temperature for up to 5 days.Freeze unfilled cookies for up to 2 months.