Preheat your oven to 350℉ (177℃) and prepare baking sheets with parchment paper or silicone mats.

Melt the chocolate chips and butter in a microwave-safe bowl until smooth and glossy. Cool slightly.

In a stand mixer, beat the light brown sugar, granulated sugar, and eggs on high speed until light and pale.

Add melted chocolate and vanilla extract, and mix until well combined. Include espresso powder if using.

Add flour, cocoa powder, and salt; mix on low speed until just combined.

Scoop the batter onto prepared sheets, leaving space for spreading.

Sprinkle flaky sea salt on top of each scoop if desired.

Bake for 13-14 minutes until edges are set but centers remain soft.

Cool on the pan for 5 minutes before transferring to a wire rack to cool completely.