Step 1

Preheat the oven to 350 degrees F. Line baking sheets with parchment paper or silicone baking mats.

Step 2

In a medium bowl sift the flour, cocoa powder, baking powder, espresso powder, and salt.

Step 3

In a large bowl use an electric mixer to beat the butter, granulated sugar, and brown sugar on medium-high speed until light in color and smooth. Add the egg and egg yolk and beat until combined. Add the vanilla extract. On low speed gradually add flour mixture. Fold in the chopped chocolate with a rubber spatula.

Step 4

Using a spoon or spring-loaded scoop, drop 1 ½ - tablespoon sized balls of dough onto the prepared baking sheets.

Step 5

Bake for about 10 minutes. Let cool on baking sheets for 5 minutes before removing to wire wracks to cool completely. Cookies can be stored in an airtight container at room temperature for 3 to 4 days.