Preheat the oven to 350. Grease two 8x4 pans.
In a small bowl, mash bananas. Set aside.
In a large bowl, cream butter, sugar, and brown sugar together until light and fluffy.
Add in the eggs, one at a time, beating well after each addition. Add in vanilla extract, and mix.
Sift together the flour, baking soda, and salt in a separate bowl. Slowly incorporate the dry ingredients into the wet ingredients, and stir until just combined.
Add in mashed bananas, and mix until combined. Pour into prepared loaf pans.
Bake for 35-40 minutes, or until a cake tester comes out clean with just a few moist crumbs stuck to it.
Allow to cool for 10 minutes. Move to a wire cooling rack.