Melt chocolate and butter in a small bowl set over a pot of simmering water.

Stir until melted and smooth.

When chocolate is melted, remove the bowl from the heat and set it aside to cool.

Preheat oven to 350 degrees.

Line 2 sheet pans with parchment paper or Silpat and set aside.

Put flour and baking powder in a small bowl and whisk together to combine, set aside.

Crack eggs into the bowl of a stand mixer, whisk gently.

Add granulated sugar, instant espresso powder, vanilla extract, and kosher salt.

Beat on medium-high speed for 11-13 minutes. Don’t skimp on the time. You’re beating lots of air into the batter, which is going to help the cookies poof up and give them a wonderful texture. You will notice your batter going from very thin to being much thicker and fluffier.

When your batter is well beaten, remove the mixing bowl and beater from the stand.

Pour in the melted chocolate and butter mixture.

Give it one or two stirs to get it started mixing.

Scrape the beater to the bottom when you do this. This helps loosen the chocolate up a bit.

Reattach the bowl to the stand and beat on medium-high for 2-3 minutes to thoroughly incorporate the chocolate. As the chocolate mixes in, the batter will get darker. After about 2 minutes, your batter should be dark, glossy, and thick.

Add in flour mixture and fold into chocolate mixture. Keep folding in until completely combined.

Add white chocolate chips and mix till combined.

Drop rounded tablespoons of batter onto your prepared pans.

Bake for 10-12 minutes until the cookies just start to crack at the top.

Cool on pan for 5 minutes and move to a cooling rack.