Chocolate Chip Pumpkin Bread

2 cups all purpose flour
1 teaspoon baking soda
1 teaspoon baking powder
1 teaspoon salt
1 1/2 teaspoons ground cinnamon
1/4 teaspoon nutmeg
1/2 cup (1 stick) unsalted butter, room temperature
1 cup dark brown sugar plus 1 tablespoon
2 large eggs, room temperature
1 cup cooked pure pumpkin or winter squash (butternut, acorn, delicata, etc...)
1 1/2 teaspoons grated lemon peel
1 teaspoon vanilla extract
2/3 cup peach, pumpkin, strawberry, vanilla, or raspberry yogurt (or sour cream)
1/2 cup buttermilk
1 1/2 cups chocolate chips
1 cup chopped walnuts (optional)


Position rack in center of oven; preheat to 325°F. Butter 9x5x3-inch metal loaf pan. Sift first 7 ingredients into medium bowl. Using electric mixer, beat butter in large bowl until light. Gradually beat in 3/4 cup sugar. Beat in eggs 1 at a time. Beat in pumpkin, lemon peel and vanilla. Whisk yogurt and buttermilk in small bowl. Beat flour and yogurt mixtures alternately into batter in 2 additions each. Fold in chocolate chips and nuts. Transfer batter to pan; smooth top. Sprinkle with 1 tablespoon sugar.
Bake bread until tester inserted into center comes out clean, about 40-50 minutes. Cool in pan 10 minutes. Turn out onto rack; cool. (Can be made 2 days ahead. Wrap in foil; store at room temperature.)