Preheat the oven to 350°F (177°C). Line a 12 cup and a 6 cup muffin pan with liners.
Whisk the flour, baking soda, cinnamon, nutmeg, and salt together. Set aside.
Using a stand mixer with paddle attachment (or a hand mixer) blend together the oil and sugars. Then add the eggs, sour cream, vanilla, and buttermilk. Then slowly blend in the dry ingredients. Mix until fully incorporated (don't over-blend). Finally add bananas and blend together with a spatula.
For more flavor consider adding 1/2 cup chocolate chips or walnuts to the batter.
Pour/spoon the batter into the liners – make sure to fill only 2/3 full to avoid spilling over the sides. Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
While cupcakes are cooling, make the frosting. In a large bowl using a hand mixer or with a stand mixer beat the butter and sour cream together until creamy. Slowly add the flour and blend until completely mixed. Then add vanilla and blend again.
You can frost these cupcakes however you would like to. However I prefer to pipe my cupcakakes. For the cupcakes picture here I used the Aetco 808 large round tip.