Preheat oven to 350. In a medium bowl, beat butter till creamy. Add the sugar 1/3 cup at a time, beating after each addition. Add eggs, one at a time, continuing to beat. Mix in the vanilla and bananas.
Sift together flour, baking powder and soda, and salt. Add creamy mixture, a little at a time, alternating with milk. Fold in chopped cashews. If you overbeat this, you will end up with tough bread.
Butter and flour a large loaf pan. Pour in batter. Bake 1 hr or until tests clean with a toothpick.