ah-mazing banana muffins

These muffins (via Martha Stewart) are so good - the sour cream  makes them moist and even more delicious. Make these soon, you won't be disappointed!

1/2 cup (1 stick) butter, at room temperature, plus more for pan
1 cup granulated sugar
2 large eggs
1 1/2 cups unbleached flour
1 teaspoon baking soda
1 teaspoon salt
2 medium sized mashed very ripe bananas
1/2 cup sour cream
1 teaspoon vanilla
1/2 cup chopped walnuts or pecans

• Preheat oven to 350 degrees. Butter a 12 cup muffin pan; set aside. In an electric mixer fitted with the paddle attachment, 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 the butter mixture, and mix until just combined. Add bananas, sour cream, and vanilla; mix to combine. Stir in nuts, and pour into prepared muffin pan. Bake until a cake tester inserted into the center of a muffin comes out clean, about 25 minutes. Let rest in pan for 10 minutes, then turn out onto a rack to cool.