Step 1

Preheat the oven to 350°F. Line an 8-inch square baking pan with foil or parchment, allowing the foil or parchment to extend over the rim of the pan by 2 inches. Spray with cooking spray.

Step 2

In a small bowl, whisk the flour, baking powder, and salt; set aside. In a medium saucepan, melt the butter over low heat. Remove the saucepan from the heat. Whisk in the cocoa and vanilla; let stand for 5 minutes. Add the granulated sugar, brown sugar, egg, and egg whites to the cocoa mixture; whisk until blended. Stir in the flour mixture until blended. Stir in 1/2 cup of walnuts.

Step 3

Scrape the batter into the baking pan and spread evenly. Scatter the remaining 1/4 cup of walnuts over the batter. Bake until a toothpick inserted into the center comes out with moist crumbs clinging, 20 – 25 minutes. Let cool completely in the pan on a rack. Lift from the pan using the overhanging foil or parchment as handles; cut into 16 squares.

Step 4

Serving size: 1 square.