Adapted from The Mom 100 Cookbook
1 cup (2 sticks) salted butter
Nonstick cooking spray
3 ounces unsweetened chocolate
1⁄2 cup unsweetened Dutch-processed cocoa powder
21⁄2 cups granulated sugar
1⁄4 teaspoon kosher or coarse salt
1 tablespoon pure vanilla extract
1 1⁄2 cups flour
Preheat the oven to 350. Spray a 13 by 9–inch baking pan with nonstick cooking spray.
Place the butter and chocolate in a large microwave safe bowl and zap at 30 second increments, stopping and stirring till melted and smooth. Stir in the cocoa powder, sugar, and salt, then blend in the vanilla. Beat in the eggs one at a time, stirring to mix quickly so they don’t have a chance to cook at all before they are blended in. Blend in the flour.
Scrape the thick batter into the prepared baking pan and smooth the top with a spatula. Bake until the edges just begin to pull away from the sides of the pan and a toothpick inserted into the middle comes out clean, 25 to 30 minutes.
Let the brownies cool in the pan on a wire rack. When completely cool, cut them into 12 or 24 squares.