Move rack to center of oven and preheat 350° F. Spray a 9x13" baking pan with cooking spray.
In a microwave-safe medium-sized bowl, melt butter and chocolate on medium-high power until melted, approximately 3 minutes. Stir until smooth.
Mix in granulated sugar and eggs (one at a time) with a wire whisk.
Mix in vanilla and almond. Fold in walnuts. Combine flour, baking powder, and salt and fold into chocolate.
Spread batter into greased 9x13" pan and bake in preheated oven at 350°F for about 33-35 minutes (depending on your oven). Do not over-bake! A toothpick inserted into the center may have some chocolate fudge on it, but not wet batter.
Cool pan on wire rack for at least 15-30 minutes before removing.