Preheat oven to 325°F. Fit a piece of parchment paper to the bottom of an 8x8x2 ovenproof baking dish, allowing several inches to overhang on two sides. This will be used to lift the finished brownies from the dish after they have baked Spray the dish and parchment paper with cooking oil.

In a large saucepan set over low heat, add the chocolate and butter. Stir constantly until they are melted. Remove the saucepan from the heat and add the cocoa powder, espresso powder, sugar, and salt. Stir until well combined. Let cool slightly, then gradually stir in the beaten eggs and the vanilla extract.

Add the flour and stir until blended. Set aside 2 tablespoons of the cocoa nibs and fold the remainder of the nibs into the batter. Pour the batter into the prepared baking pan. Sprinkle the top with the additional 2 tablespoons of cocoa nibs.

Bake the brownies in the center of the oven for 30-35 minutes. An instant-read thermometer should read 193°F to 200°F when inserted in the center. It may still be a little jiggly in the center but it will firm up as it cools. Transfer to a cooling rack.

Once cool, loosen the edges with a sharp knife and lift the entire brownie out of the dish with the parchment paper. Slice the brownies into 16 squares with a sharp knife dipped in hot water and wipe clean after each slice. These freeze well.