Preheat the oven to 350°F.
In a small bowl combine the flour, cocoa powder, baking powder and sea salt; set it aside.
Grease a 9X13 inch baking pan.
Melt the butter in a pan on the stovetop or in the microwave, as preferred.
Pour the butter into a mixing bowl. Stir in the sugar and vanilla. Add the eggs one at a time, beating in each addition. Add the flour mixture and combine. Stir in nuts or chocolate chips, if desired.
Pour the batter into the baking pan. Bake for 30-35 minutes. Cool the brownies in the baking dish completely before slicing.