Banana Cake

2 cups flour
1 tsp. Baking powder
1 tsp. Baking soda
2 tsp. Salt
1 1/2 cups sugar
1 egg plus 2 egg yolks
1 cup mashed bananas
3/4 cup sour- or buttermilk
1 tsp. Vanilla
1 cup chopped nuts

Sift flour, baking powder, baking soda, and salt together. Cream butter thoroughly, add sugar gradually until light and fluffy. Add eggs and beat well; then add bananas and beat again. Add flour to creamed mixture alternately with milk, a small amount at a time, beating after each addition, until smooth. Add vanilla and nuts. Bake in greased pans for 25 minutes at 375 degrees.