Preheat oven to 350 degrees. Butter and flour a 9-inch nonstick tube pan. In a medium bowl, whisk together flour, baking powder, and salt; set aside. In a small bowl, whisk together sour cream and baking soda.
With an electric mixer, beat butter, sugar, eggs, and vanilla on high speed until light and fluffy, about 5 minutes. With mixer on low speed, add flour mixture in three additions alternately with sour-cream mixture in two, beginning and ending with flour. Mix just until moistened.
Spread a third of the batter in pan; sprinkle with a third of topping. Repeat twice, ending with topping. Bake until a toothpick inserted in center comes out with a few moist crumbs, 60 to 70 minutes.
Cool in pan 30 minutes. Turn out of pan; cool, top side up, on a rack.