Cream together butter and sugar. Add in egg and beat until light and fluffy. Roughly mash the bananas with a fork and add in vanilla, greek yogurt, cinnamon, and salt. Mix into the sugar mixture.
Combine together dry ingredients: flour, baking powder, baking soda and any add ins like walnuts. Fold into the wet mixture until evenly combined.
Pour mixture into a small baking pan and bake for about 45 minutes or when a toothpick inserted comes out clean.