Preheat oven to 350° F.
In bowl of electric mixer, cream butter, and blend in the sugar. Add eggs, one at a time,beating well after each addition.
Blend in the sour cream.
If using Wondra, or another pre-sifted flour, no need to sift. Just measure exactly three cups, then sprinkle the baking power on top and mix it in gently; so ,when you add the flour to the butter-sour-cream-egg mixture, the baking powder will be distributed somewhat evenly. (If not using a pre-sifted flour, sift flour; measure; then sprinkle the baking powder on top and mix it gently into the flour.)
Add flour mixture in 4 or 5 parts to first mixture, blending well.
Pour batter into a buttered 9-inch tube pan, or Bundt pan.
Bake in 350° F. oven for about 1 hour 25 minutes, or until it tests done by inserting a wooden toothpick.
Let stand for 5 minutes; then invert on a cooling rack. Allow to cool completely. Then, wrap tightly in plastic wrap or foil and leave for about 24 hours at room temperature before slicing.