We've used this standby for years:
Mayonaisse Chocolate Cake
2 cups flour
1/2 cup cocoa
1 1/2 teaspoons baking soda
1/4 teaspoon salt
1 cup sugar
3/4 cup mayonnaise
1 cup water
1 teaspoon vanilla
(We also add about 1 Tabelspoon of red food coloring to make it look extra rich)
PREPARATION:
Sift together the flour, cocoa, soda and salt. Cream together the sugar, mayonnaise, water and vanilla. Add dry ingredients to the creamed mixture; stir until well blended. Pour batter into greased and floured layer cake pans (or a 9- x 13-inch pan). Bake at 350 degrees F for about 25 minutes or until it passes the toothpick test...
(It's our U.S. recipe, you'll have to do the conversions)