In the bowl of a standing mixer, beat the butter and sugar for 3 – 4 minutes until light and fluffy. Beat in the eggs one at a time, then mix in the vanilla. Gradually add flour mixture, mixing until combined. Beat in the pineapple and bananas. Pour into cupcake pan, about 3/4 of the way full. Bake for 17 – 20 minutes, until tops are golden brown and a toothpick comes out clean. Remove and let cool on wire rack before frosting.