Preheat the oven to 350°F.
Grease a loaf pan and set aside.
In a large bowl, cream together the melted butter and sugar.
Mix in the mashed bananas, stirring until well combined.
Slowly mix in the flour and baking powder, stirring until well combined.
Fold in the berries until just mixed.
Bake for 55-60 minutes.
Let cool before slicing and serving.