Preheat the Oven – 325°F
Mash – Using a fork mash the ripe bananas in a bowl.
Combine Dry Ingredients – In a mixing bowl, combine flour, baking soda, cinnamon, nutmeg and salt. Set aside.
Whip Sugar and Eggs – Then, using the whip attachment, combine the sugar and eggs in a stand alone mixer and mix on medium for 5 minutes until light and fluffy.
Add Oil and Butter – Turn the mixer to low and very slowly add in the oil and melted butter. Should take about 1 minute to add these in, slowly whipping to incorporate.
Add Bananas, Sour Cream and Vanilla – Mix on low for another minute.
Fold in the Dry Ingredients – Using a rubber spatula, gently fold in the dry ingredients into the wet. Do this just until the ingredients are incorporated, but do not beat or over mix.
Prepare – Cut a piece of parchment paper long enough to hang over the sides of a 9×5 loaf pan. Butter the pan, then place the parchment paper over the top. Butter the parchment paper and all sides of the pan. Pour the batter into the pan.
Bake for 1 hour, then check the center. If it’s still jiggly or not fully set, continue baking in 10-minute intervals until the center is fully cooked and no longer sinks. Total bake time can vary between 1 hour to 1 hour and 30 minutes, depending on your oven.