Preheat the oven to 350 degrees, and line two baking sheets with parchment paper or a non-stick sheet.

In a medium bowl, whisk together the flour, cocoa powder, baking soda, baking powder, salt, and espresso powder. Set aside.

In a large bowl, beat together the melted butter, brown sugar, and 3/4 cup sugar.

Mix in the vanilla extract, egg, egg yolk, and coffee.

Slowly add in the flour mixture, and stir until completely combined.

Scoop rounded tablespoonfuls of the dough into your hands, and roll into a ball. In a small bowl, mix the 1/2 cup sugar and 1 tsp. espresso powder. Roll each dough ball in the sugar mixture to coat.

Place on your baking sheet, and press down each dough ball slightly with the bottom of a glass.

Bake for 8-10 minutes, or until the cookies are set and have cracks on the edges and top.