Preheat oven to 350°F (175°C). Grease or line a 9×5-inch loaf pan.

In a large bowl, cream butter and sugar until light and fluffy.

Add eggs one at a time, then mix in mashed bananas and vanilla extract.

In a separate bowl, whisk together flour, baking soda, and salt.

Gradually stir dry ingredients into the banana mixture. Add milk or sour cream if using.

Fold in nuts if desired.

Pour batter into prepared loaf pan and smooth the top.

Bake for 55–65 minutes, or until a toothpick comes out clean from the center.

Cool in pan for 10 minutes, then transfer to a wire rack to cool completely.