Step 1

Make the cookies: In a large bowl, beat the butter and sugars with an electric mixer on medium until light and creamy, about 3-4 minutes. Scrape the bottom and sides of the bowl and beat again until smooth.

Step 2

Blend in the egg and yolks, one at a time, until combined, then add the vanilla.

Step 3

In a separate bowl, whisk the flour, cocoa powder, baking powder, baking soda, and salt until evenly distributed.

Step 4

Gradually stir the dry ingredients into the butter mixture by hand with a spatula until just before the dough comes together. Fold in the chocolate chips, then cover the bowl and chill the dough in the fridge for at least 3 hours or overnight.

Step 5

When ready to bake, preheat the oven to 350°F. Line two baking sheets with parchment paper.

Step 6

Scoop the dough into 1 tablespoon-sized (1-inch) balls and arrange on the baking sheets about 2 inches apart. Press a few semi-sweet chocolate chips into the tops of the cookie dough, if desired.

Step 7

Bake for 8-10 minutes until the edges are set. Let the cookies cool on the baking sheets for 5-10 minutes before transferring to a wire rack to cool completely.

Step 8

Make the filling: In a large bowl, beat the butter until smooth. Add 1 cup powdered sugar and mix on low until blended. Mix in the salt and vanilla, then add more powdered sugar, as needed, until the desired thickness is reached. Add the cream, 1 teaspoon at a time, if needed to thin it.

Step 9

Assemble: When the cookies are completely cooled, dollop or pipe about 1-2 tablespoons of the filling in the center of half of the cookies. Sandwich them together with the plain cookies, pressing gently to spread the filling. Then serve and enjoy!