Move oven rack to center and preheat oven to 350 degrees F. Line a 9×13“ metal baking pan with parchment paper.
In microwave oven, on medium-high power, melt butter and chocolate in 2-quart microwave-safe bowl, about 3 minutes. Stir until smooth. Mix in granulated sugar, then beat in eggs, one at a time, with wire whisk.
Mix in vanilla and almond. Stir in nuts, if using them. Combine cake flour, baking powder, and salt and fold into chocolate. Spread batter in 9×13” pan lined with baking parchment and bake in preheated oven at 350 degrees F for about 33-35 minutes. Do not overbake; toothpick may have fudgy crumbs on it, but not wet batter.
Cool pan on wire rack for 15 minutes before removing (if you wish) brownies from pan.