Combine the cake ingredients and bake in a 9x13 pan in a 350 degree oven for 40 minutes, or until a toothpick is inserted and comes out clean.
Mix together peanut butter and 3/4 tsp of cooking oil. Spread this mixture on top of cooled cake. Refrigerate for 20 minutes.
Heat in a saucepan 1/4 cup of cocoa, powdered sugar, sour milk, butter, and vanilla.(you can sour the milk with vinegar, add about a half a tsp of vinegar to the milk and it should thicken you may need a dab more) Mix this until smooth and comes to a boil. Let cool for a few minutes... Pour and spread over the peanut butter layer. Cool and keep refrigerated.