Preheat oven to 350 degrees F. Butter and flour a 9 by 5-inch loaf pan.
In a large bowl, beat butter and sugar at medium speed with an electric mixer until creamy. Add eggs, vanilla and buttermilk, beating well.
In a small bowl, combine flour, baking powder, and baking soda. Slowly add to the wet ingredients. Add mashed bananas and fold in raisins. Pour into prepared pan and bake for 50 to 60 minutes. Let cool in pan 10 minutes. Remove from pan and let cool completely on a wire rack.
Cut banana bread into slices. Spread peanut butter over half of banana bread slices. Top with remaining slices to make a sandwich. Cut each sandwich into desired shapes or sizes. Roll edges in chopped peanuts and serve.