• Preheat oven to 325°. Grease 4 mini loaf pans or 2 large loaf pans. Dust greased loaf pans with cinnamon sugar if desired(Optional).
• In a large bowl, cream butter and sugar together. Mix in eggs, mashed bananas, sour cream or yogurt, vanilla, cinnamon, and nutmeg.
• Add flour, baking soda, and salt. Mix just until dry ingredients are wet. Don't over-mix. Fold in walnuts if using. Divide into prepared pans. Don't fill pans more than 2/3 full or they may overflow. Use more pans if needed or cook the excess batter in muffin tins.

Crumb Topping

• In a small bowl mix brown sugar, flour, cinnamon, and butter together with a fork or pastry cutter until coarse crumbs are formed. Sprinkle crumbs on top of the prepared batter.
• Bake for around 50 minutes to 1 Hour 15 minutes, or until a knife or toothpick inserted in the center comes out clean. You can cover it with tin foil for the last 15 to 20 minutes to prevent the edges from getting too dark. Smaller pans may take less time while larger pans may take a little longer.