Chocolate mayonnaise cake is a moist and fudgy chocolate cake made with mayonnaise. Top this cake with a light and fluffy chocolate frosting for a wonderfully decadent chocolate cake.
Place a larger mesh strainer over a mixing bowls. Add the all purpose flour, sugar unsweetened cocoa powder, baking soda and salt. Sift the dry ingredients into the bowl. Then whisk the dry ingredients together until well combined.
Add the mayonnaise, vanilla and very warm coffee or water into the dry ingredients. Whisk the ingredients together to combine. Then whisk more vigorously to fully combine the wet and dry ingredients. The chocolate mayo cake batter should be smooth, slightly thick and glossy. Evenly spread the chocolate cake batter into the prepared pan.
Bake the mayonnaise chocolate cake for 30 - 35 minutes or until a toothpick inserted into the center of the chocolate cake comes out clean with a few moist crumbs. If the wet batter comes out coating the toothpick, bake an additional 3 - 5 minutes before checking again.
Cool the cake in the pan for 20 minutes. Run a butter knife around the edges of the cake that touch the pan. Gently lift the chocolate cake out of the pan using the parchment paper. Transfer to a cooling rack or serving plate to cool to room temperature.
Cream the butter on medium speed until smooth and creamy. Mix in the cocoa powder, powdered sugar, vanilla extract, 1 teaspoon milk and salt. Mix on low until mostly combined. Increase the speed to medium for 1 minute.
Evenly spread the fluffy chocolate buttercream on top of the cooled chocolate cake. Use the back of a small spoon to create some decorative swirls and swoops if you like! Slice and enjoy.