Preheat the oven to 325°F . Butter an 8-inch square baking pan. Line the pan with parchment paper leaving longer pieces to hang over the sides to help remove the brownies; set aside.

Melt the butter and chocolate together in a 2-quart saucepan over low heat, stirring constantly. Stir in the espresso (or coffee). Remove the pan from the heat and stir in the sugar. Add the eggs and vanilla and stir to make a smooth batter. Add the flour, salt, and stir until incorporated.

Pour the batter into the prepared baking pan and spread evenly. Bake until a toothpick inserted in the center comes out clean, 40 to 45 minutes (i checked mine at about 38 minutes and they were done. Every oven is different so you may want to check yours at around 35 minutes).