Make a well in the center of the dry ingredients. Add in the cornstarch water mixture, the homemade buttermilk, the warm water, vegetable oil and vanilla. Whisk until smooth and combined.
Once the cakes have cooled completely, take them out of the pan and slice the tops off to create flat surfaces.
Cut or crumble the tops to make tiny crumbs. We will use these later so set them aside.
Place one layer of cake on the bottom of a cake plate/stand and pipe a ring around the top edge of the cake. This is to prevent the pudding from oozing out.