Using a handheld or stand mixer fitted with the paddle attachment beat the butter and brown sugar on high speed until smooth and creamy (about 2 minutes). Then, add the eggs, one at a time, while beating well on medium speed after each addition. Beat in the yogurt, mashed bananas, and vanilla extract until combined. Turn the mixer on low speed and slowly beat in the dry ingredients into the wet ingredients. Careful not to over mix. Fold in the nuts or chocolate chips, if using.