the chips and oil, then microwave on HIGH (100%) for 45 seconds, stirring if necessary. If necessary, microwave on HIGH (100%) for an additional 15 seconds or until melted and smooth when stirred. Gradually add the peanut butter to the vanilla batter, blending well. Pour the peanut butter batter into the prepared pans. Randomly place spoonfuls of the chocolate batter on top and swirl in as directed on the cake package. Bake for 30 to 40 minutes or until a wooden pick inserted in the center comes out clean. Cool 15 minutes, in the pans, on a wire rack then remove from the pans and cool completely. Frost as desired.