Preheat oven to 350°. Grease or line a 9"x 13" pan with parchment paper.
Blend melted butter, sugar, and vanilla in a mixing bowl. Add eggs, and beat the mixture together well with a spoon.
Combine flour, cocoa, baking powder, and salt. Gradually add dry ingredients to the egg mixture until blended. Don't over-mix. Spread into prepared baking dish.
Bake for 20 to 25 minutes, until the brownie begins to pull away from the edge of the pan. Cool in pan on rack.