Preheat oven to 350°F (175°C).

Grease and flour a loaf pan.

Prepare sour milk by adding 1/2 teaspoon vinegar to 4 tablespoons of milk and let stand for 15 minutes.

Cream together the butter and sugar until light and fluffy.

Beat in the eggs one at a time.

Stir in the sour cream or sour milk.

In a separate bowl, combine the baking soda, salt, baking powder, and flour.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the crushed bananas and chopped nuts.

Pour batter into prepared loaf pan.

Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.

Let cool in pan for 10 minutes before transferring to a wire rack to cool completely.