Instructions
Preheat the oven to 350 degrees. Line the cupcake pans with paper liners or grease the sheet cake pan with butter. (If you will be making a layered cake, see further directions below.)
Combine all dry ingredients in a mixing bowl and whisk to combine. Add the sour cream and olive oil and beat to combine. Slowly add the water and continue beating. Add the vanilla and the vinegar, beat again. Add the egg and beat to combine.
Pour into the prepared cake pans or fill the cupcake liners. Bake the cupcakes for 18 minutes and the cakes until an inserted toothpick comes out with moist crumbs, 28-30 minutes for a half-sheet pan. Let the cakes cool (in their pans) COMPLETELY before frosting them.
Directions For A Layered Cake
Generously butter the bottom and sides of two 8″ round cake pans. Trace the bottom of the pans onto wax paper or parchment with a pencil and then cut out the circles. Place the paper in the bottom of each pan and butter the paper.
Remove from the oven and let the cake cool in the pans for 20 minutes or so. Very carefully, invert the cakes onto wire racks and let them cool COMPLETELY. These are very soft cakes. Once they are completely cool, wrap in saran wrap and freeze for a couple hours before assembling the cake.
To frost the cake, place one layer of the very cold cake flat side up on a serving plate or stand. Spread about ½ of the Peanut Butter Frosting evenly over the top. Place the second layer on top and frost the top and sides with all but about ½ a cup of the remaining frosting.
With this cake, it is a good idea to make a crumb coat with the first layer of frosting. Basically, just make sure the cake is covered in frosting, even if a few stray crumbs show through. Chill the assembled cake again (place it back in the freezer for half an hour or so) before you add the last bit of frosting. Use the remaining bit of frosting to create a smooth final coating.
Notes
If you make the frosting in advance and store it in the refrigerator, allow several hours for the frosting to return fully to room temperature again before frosting the cupcakes.
