Preheat your oven to 350°F (175°C).
Grease and flour a 9-inch round cake pan or line it with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg (if using).
In a large bowl, cream the softened butter and granulated sugar together until light and fluffy.
Beat in the eggs, one at a time, until well combined.
Mix in the mashed bananas until smooth.
Gradually add the dry ingredients to the banana mixture, alternating with the sour cream or yogurt. Begin and end with the dry ingredients. Mix until just combined.
Stir in the vanilla extract.
Pour the batter into the prepared cake pan and spread it evenly.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
Enjoy your meal!