Preheat oven to 350 degrees, grease and flour a 12 cup bundt pan or 10 inch angel food tube pan
Sift flour, cocoa and salt together.
Cream butter and sugar until light. Add sour cream and bananas to butter and sugar.
Beat the egg until well blended. Slowly, beat eggs into butter/banana mixture. Blend in half the flour mixture.
Stir in milk and remaining flour. Mix only until evenly blended. Be careful not to over mix batter.
Spoon into prepared pan and bake 30 minutes on the lowest level of your oven rack. Rotate cake moving the back to the front and bake until toothpick pulls out clean about 30 more minutes. Let cool in pan about 5 minutes on rack.