Preheat oven to 350 degrees. Grease and flour loaf pan. In large bowl cream butter. Add sugar and continue to beat until light. Add vanilla, eggs and mashed banana and combine thoroughly. Combine flour, baking powder and soda. Add the flour mixture to the creamed mixture, alternating with the buttermilk. Fold in the chocolate chips. Bake for 50-60 minutes or until center is firm. Cool in pan for 10 minutes. Remove and cool completely.