Line two baking sheets with parchment paper and set aside.

Add flour, cocoa powder, salt and baking powder to a medium sized bowl. Whisk to combine, then set aside.

Add butter, brown sugar and granulated white sugar to a large bowl. Cream together with an electric mixer for two minutes.

Add the egg yolks and vanilla to the butter/sugar mixture and mix until pale in color and fluffy, 1-2 minutes.

Add in the dry ingredients and mix just until combined.

Scoop the dough into 34 portions, then roll into balls. (About 1 tablespoon of dough.)

Transfer the dough to the baking sheets.

Using a ¼ tsp, press down on the dough balls to create an indent.

Chill the prepared indented dough balls for at least one hour.

Preheat the oven to 350 degrees.

Arrange the prepared dough about 1 ½ inches apart on the baking sheets.

Bake the cookies for 9-11 minutes. (I think 10 minutes is perfect.)

When the cookies are done baking, lightly press down on the centers again with a ¼ tsp.

Let the cookies cool on the baking sheet for 5 minutes. Transfer them to a cooling rack to completely cool.

Add the chocolate chips to a small bowl.

Heat the heavy cream in the microwave, or on the stove, until just about boiling.

Pour the heavy cream over the chocolate chips and let sit for 1 minute.

Stir to combine the cream and chocolate together.

Fill each well of the cookies with about 1 teaspoon of ganache, more if it'll fit.

Sprinkle sprinkles over the cookies if you wish.

Chill the cookies in the fridge for 10-15 minutes to allow the ganache to set.

Store left overs in an air tight container for up to three days.