Preheat the oven to 350. Spray a 9 X 13" baking pan with cooking spray, then line it with parchment paper so the parchment hangs over the sides (you can lift the brownies out of the pan). Spray the parchment paper.
Heat the butter in a large skillet until it foams and continue to cook on medium, stirring constantly until it starts to brown. The butter will have foam on top so watch carefully to make sure the solid bits on the bottom do not burn; you should also notice a distinct scent as it starts to brown. An amazing one too!
Let the butter cool before continuing.
Combine the butter, sugar and vanilla in a mixing bowl until blended. Add eggs, one at a time, beating well after each addition.
Add cocoa powder to the bowl, mix on low speed until well blended.
Combine the flour, baking powder, salt and espresso in a bowl and whisk. Add them to the mixture in the mixing bowl and beat well.
Stir in the toasted nuts and pour the mixture into the prepared pan.
Bake 25-35 minutes or until a toothpick comes out clean. Do NOT overbake.
Let cool and cut into squares.
Serve with a scoop of vanilla ice cream and fresh raspberries.