Preheat oven to 350 degrees F. You can bake this cake in 2 6 inch cake rounds, in muffin tins, or in 3 small tins. Oil the pans you decide to use.
Whisk together all wet ingredients. Add dry ingredients and fold in chopped apple.
Bake for 15 minutes or less or more time depending on what kind of pan you use.
Mix together yogurt and peanut butter. Frost cooled cake.