Prepare Pan – Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan, line with parchment paper.

Mix Dry Ingredients – In a bowl, whisk flour, baking soda, baking powder, salt, and cinnamon.

Cream Butter and Sugar – Beat softened butter, granulated sugar, and brown sugar until fluffy (about 2 minutes).

Add Wet Ingredients – Beat in eggs one at a time. Add vanilla and mashed bananas. Mix in sour cream or yogurt.

Combine – Fold dry ingredients into wet mixture gently until just combined.

Assemble – Pour half the batter into pan. Sprinkle with half the cinnamon-sugar topping. Add remaining batter and top with the rest of the topping. Swirl lightly with a knife if desired.

Bake – Bake 55–65 minutes or until a toothpick inserted comes out clean. Tent with foil if top browns too quickly.

Cool & Serve – Cool 10 minutes in pan. Remove and cool fully on a wire rack before slicing.