Preheat oven to 325°F.

Heat butter in a large skillet or pot over medium heat.

Cook butter until lightly golden brown and bubbly. Add your walnuts and vanilla and stir to combine and remove from heat.

Add your dark chocolate and stir to melt.

In another bowl, whisk together the eggs, white sugar, and salt until light and fluffy.

In a medium bowl, sift together the dark cocoa powder, espresso powder, AP flour, and baking powder.

Add your melted chocolate, walnuts, and butter mixture to your egg mixture and combine.

Add your dry ingredients and fold in with a spatula until no streaks are left.

Grease and line an 8x8 square baking sheet with parchment paper. Pour in your brownie batter and spread with a spatula evenly.

Bake for 30 - 40 minutes until a toothpick comes out half clean. The top should be shiny and cragged and still a little gooey in the center.

Let rest for 20-30 minutes and dust with powdered sugar, slice, and serve.