Thin Mayo Chocolate Bar Brownies

4 ingredients•Prep: 10 mins•Cook: 28 mins

Ryan Tyler Cooks

•

July 10, 2026

Ingredients (4)

For most boxed brownie mixes:* Replace the eggs completely.* Replace the oil completely.* Use ½ cup mayonnaise in place of: * 2 eggs + ½ cup oilIf your brownie mix calls for:* 2 eggs + ⅓ cup oil → use about ⅓ cup mayonnaise* 3 eggs + ½ cup oil → use about ⅔ cup mayonnaiseThe mayonnaise provides both the fat from the oil and the moisture and emulsification from the eggs, resulting in extra moist, chewy brownies

Prepare the Pan Preheat the oven according to the brownie mix package directions, typically 350°F (175°C).Lightly grease or line an 8x8-inch baking pan with parchment paper
Make the Batter In a large mixing bowl, combine the brownie mix, mayonnaise, and water.Stir until smooth and fully incorporated. Do not overmix
Create the Chocolate Center Pour half of the brownie batter into the prepared baking pan and spread evenly.Place the chocolate bar directly in the center of the batter. If needed, break the chocolate bar into large sections so it fits comfortably while remaining concentrated in the middle.Carefully spread the remaining brownie batter over the chocolate bar until fully covered
Bake according to the package directions, usually 25–30 minutes, or until the edges are set and a toothpick inserted near the edge comes out with a few moist crumbs.Avoid testing directly over the chocolate center
Cool Allow the brownies to cool for at least 20 minutes before slicing.As they cool, the chocolate bar will remain soft and gooey in the center