Line the baking pan with parchment and lightly grease it. This prevents sticking and allows easy removal.

Whisk flour, baking powder, baking soda, and salt in a bowl. Set aside.

Beat butter with both sugars until light and fluffy. This step builds air and helps create a tender crumb.

Mix in eggs one at a time, followed by vanilla. Scrape down the bowl to ensure even mixing.

Stir in mashed bananas and sour cream or yogurt. The batter may look slightly curdled at this stage, which is normal.

Fold in the dry ingredients gently, mixing just until combined. Overmixing leads to toughness.

Spread batter evenly in the pan and bake until a toothpick inserted in the center comes out clean or with a few moist crumbs.

Allow the cake to cool fully before frosting. Warm cake will melt the frosting.