Mayonnaise helps keep your brownies soft and prevents them from getting too dry. Even though it sounds odd, you won't be able to taste the mayonnaise in the brownies.
Then, mix ¾ cup of flour, ½ teaspoon of salt, and 1 teaspoon of baking powder in a bowl and set it aside. Next, melt 1 cup of chocolate chips in a double boiler over medium heat.
Once the chocolate chips are melted, add the eggs, 1 teaspoon vanilla, 1 cup sugar, and ½ cup of mayonnaise and stir until smooth. Stir in the flour, and add walnuts if you wish.