Preheat your oven to 350°F (175°C) and prepare baking sheets lined with parchment paper.

In a medium bowl, whisk together all-purpose flour, baking soda, baking powder, salt, and instant espresso powder.

In a large bowl, cream together the softened unsalted butter, granulated sugar, and brown sugar until light and fluffy, about 3-4 minutes.

Add eggs one at a time, mixing well after each addition. Follow with the vanilla extract, blending until smooth.

Divide the cookie dough in half. Fold cocoa powder and half of the chocolate chips into one half to create a chocolate dough.

Incorporate the remaining chocolate chips into the plain dough, mixing gently.

Roll tablespoon-sized balls of both doughs together, forming marbled cookie balls.

Consider cooling the dough balls in the fridge for 30 minutes for thicker cookies.

Arrange the marbled dough balls on prepared baking sheets and bake for 10-12 minutes, until edges are set but centers are slightly underbaked.

Cool on the baking sheet for about 5 minutes, then transfer to wire racks to cool completely.