1 cup butter, melted
3 cups white sugar
1 tablespoon vanilla extract
1 1/2 cups all-purpose flour
1 cup unsweetened cocoa powder
1 teaspoon salt
1 cup semisweet chocolate chips
1. Preheat oven to 350 degrees F . Lightly grease a 9x13 baking dish.
2. Combine melted butter, sugar, and vanilla in a large bowl. Beat in the eggs, one at a time, mixing well after each, beat in mayo after eggs are all in. Blend thoroughly.
3. Dump flour, cocoa powder, and salt in a separate bowl, and mix together well with a fork. Gradually stir the flour mixture into the chocolate mixture until blended.
4. Stir in the chocolate morsels. Spread the batter evenly into the prepared baking dish.
5. Bake in preheated oven until an inserted toothpick comes out clean, 35 to 40 minutes. Remove, and cool pan on wire rack before cutting.
I did the blending with my hand mixer and stirring by hand, but in hind sight the kitchen-aid mixer would have made things so much easier (mine has a stir setting). The batter gets a little hard to stir once all of the flour mixture is added.