Heat oven to 350°. Line an 8 x 8-inch pan with aluminum foil; coat with nonstick cooking spray.Advertisement
In a large bowl, whisk flour, cocoa powder, baking powder and salt. In another large bowl, beat butter and sugar with a hand mixer until fluffy, about 2 minutes. Beat in eggs one at a time until well combined, then beat in vanilla.
Mix dry ingredients into wet ingredients on low speed until just combined.
Transfer to prepared pan and spread evenly. Bake at 350° for 22 to 25 minutes, until a toothpick inserted in center comes out clean. Cool 10 minutes, then lift out brownie in foil, place on a wire rack and cool completely.