Martha Stewart's Banana Bread

1/2 c butter (1 stick), at room temperature
1 c sugar
2 large eggs
1 1/2 c flour
1 tsp baking soda
1 tsp salt
1 c very ripe bananas, mashed (~3 bananas)
1/2 c sour cream
1 tsp vanilla extract
1/2 c chopped pecans or walnuts (optional)

Preheat oven to 350 degrees. Butter 9x5x3 inch loaf pan; set aside. With an electric mixer, cream butter and sugar until light and fluffy. Add eggs and beat to incorporate. In a medium bowl, whisk together flour, baking soda and salt. Add to butter mixture and mix until just combined. Add mashed bananas, sour cream and vanilla; mix to combine. Stir in nuts (if desired) and pour into pan. Bake until cake tester inserted into center of loaf comes out clean, about 1 hour. Let rest in pan for 10 minutes, then turn out onto a rack to cool.