Preheat the oven to 350 degrees F (175 degrees C). Grease an 8-inch square baking pan.

Sift flour, cocoa, and salt together in a bowl. Set aside.

Melt butter in a small saucepan over low heat. Stir in espresso powder. Stir in chocolate chips until melted. Remove from heat; mix in white sugar and brown sugar until fully blended. Add eggs and vanilla extract and mix well. Stir in the flour mixture until just combined. Pour batter into the prepared baking pan.

Bake in the preheated oven until top is dry and edges have started to pull away from the sides of the pan, 25 to 30 minutes. Do not overbake. Let cool completely before cutting into squares.