Preheat oven to 350°F. Prepare a 9×13-inch baking dish.
In a bowl, whisk together flour, cocoa powder, baking powder, and salt.
In a separate bowl, beat eggs, sugar, butter, and vanilla until light and fluffy.
Add dry ingredients and mix until combined.
Pour into prepared pan and bake for 30-35 minutes, until a toothpick comes out with crumbs but no wet batter.
Let cool completely.