Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, whisk together flour, sugar, cocoa powder, espresso powder, baking powder, and salt until combined.

In a larger bowl, beat the eggs until frothy, then mix in melted butter and vanilla extract.

Gradually fold the dry mixture into the wet ingredients until just combined, creating a stiff dough.

Gently incorporate the chocolate chips into the dough evenly.

Divide the dough in half and shape each half into a 12-inch log on the baking sheet.

Brush the tops with an egg wash and sprinkle with coarse sugar.

Bake for 25-30 minutes until firm and slightly cracked on top, then cool for 15 minutes.

Slice the logs diagonally into ¾-inch pieces and place cut-side down on the baking sheet.

Return to the oven and bake for another 15-20 minutes until crisp, flipping halfway through.

Transfer to a wire rack to cool completely for maximum crispness.