Heat oven to 180c/ gas 4 / 355f. Mix butter with dry loaf ingredients and then add in mashed bananas and other wet ingredients. Add to 13 x 23 cm loaf pan

Cut the sugars and flour with the cubed butter to make the streusel. Do this until it is crumbly but combined. Add to top or middle of loaf batter as desired

Cook for 50 to 60 minute (less if using smaller pans) until a toothpick comes out clean