Preheat oven to 350 degrees.
In a large bowl cream together butter and sugar for two minutes on medium speed.
Add in eggs one at a time, beating well after each one.
In a separate medium bowl sift together flour, baking soda and salt.
Turning your mixer onto low speed, alternate adding in the flour mixture and sour cream into the butter mixture.
Mix until flour is almost fully incorporated.
In a medium bowl, mix together mashed bananas, 1/2 of the sliced bananas and vanilla. Add into batter.
Stir until completely combined. Do not over mix.
Place about 1/2 cup mixture into each mini loaf tin that is well greased.
Line the top with 3 slices of banana each.
Bake for 20 minutes or until an inserted toothpick into the center comes out clean.
Cool in the pan for 15 minutes, then turn out onto a cooling rack and cool completely.