Cream butter and sugar until light and fluffy.
Add banana and eggs, one at a time, beating mixture after each egg.
Gradually mix in flour and vanilla.
Grease and flour a bundt pan.
Pour batter into pan.
Place pan of batter into a cold oven and bake at 300° for 120 minutes.
Do not open oven to peek during baking.
Remove from oven and invert pan on cake plate.
Cool.
Dust with powdered sugar if desired.
