Preheat your oven to 350°F (175°C). Gather and prep all ingredients.

In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt. In a large bowl, cream butter with granulated and brown sugars until light and fluffy. Beat in vanilla and egg yolk. Gradually add dry mixture until just combined.

Scoop tablespoon-sized portions of dough, roll into balls, and place on a baking sheet, spacing them 2 inches apart. Create an indentation in the center of each cookie.

Bake for 10-12 minutes until set but still soft in the center. Let cool on the baking sheet for 5 minutes before transferring to a wire rack.

Melt chocolate chips in a microwave-safe bowl. Fill each indentation with melted chocolate and allow to cool completely before serving.