Line a baking sheet with parchment paper or a silicone baking mat and set aside.
Combine chocolate chips and butter in a microwave safe container. Heat on high for 30 seconds, stir. Heat for another 15 seconds and stir again. Let the mixture sit for 1 to 2 minutes and then stir until smooth.
Stir in the espresso powder. Let the chocolate mixture cool for 15 to 20 minutes. The mixture should be thick.
Beat the eggs, sugar, and vanilla extract together at medium-high speed for 3 minutes.
Turn the mixer to low and slowly add in the cooled chocolate mixture, mixing just until combined.
Sift the flour, corn starch, cocoa powder, salt, and baking powder together in a small bowl. Stir the flour mixture into the chocolate mixture just until combined.
Stir in the mini chocolate chips. Cover and chill for at least 45 minutes.
Preheat the oven to 350F.
Scoop cookie dough with a cookie scoop and form into balls by rolling in your hand. This will ensure a uniform shape for all cookies.
Place on prepared baking sheet and bake for 12 to 14 minutes.
Let cookies cool on baking sheet for 5 minutes before transferring to a wire cooling rack.
Store in an airtight container for up to a 5 days.