Preheat oven to 350 degrees.
Grease and flour bundt pan.
Cream butter and sugar together. Add eggs one at a time, beating for a few seconds after each addition. Add mashed bananas and beat.
Combine dry ingredients in a separate bowl.
Add dry ingredients and sour cream alternately to the mixing bowl. Beat well until all combined.
Pour into bundt pan and bake for 1 hour 10 minutes or until a toothpick comes out clean.
Invert on a cooling rack and allow cake to cool slightly before slicing and serving with softened butter.