Preheat oven to 325 degrees. Line a 9x9 baking sheet with tin foil (with enough overhang on two edges that you can pull the brownies out after baking) and spray with cooking spray.
Add the eggs, one at a time, fully incorporating each one before adding the next. Whisk until mixture is completely smooth.
Pour batter into prepared pan; bake until a toothpick or cake tester inserted in center comes out with wet crumbs, 35-45 minutes (it's always 35 minutes for me).
Cool brownies in pan on a wire rack for five minutes. Use foil handles to pull brownies from pan. Cool on wire rack for at least 15 minutes.