Preheat your oven to 375 F/190 C/ 170 C fan and place large paper cases in a 12 hole muffin tin.

Sift together the flour, bicarbonate of soda, baking powder and salt and set aside.

Mash the banana in a separate bowl and add the cooled melted butter and egg and mix well.

In a third bowl, toss the fresh blueberries with two spoonfuls of the flour mixture to coat.

Add the banana mixture to the flour mixture and stir with a wooden spoon until just combined. Fold in the blueberries with any flour that might be remaining in the bottom of the blueberry bowl.

Spoon into the prepared muffin cases.

To prepare the streusel topping, combine the sugar, flour and cinnamon together and rub in the butter until the mixture resembles coarse bread crumbs.

Generously sprinkle the streusel topping over each muffin and bake, in the centre of the oven, for 20 - 25 minutes. A skewer inserted into the centre will come out clean.

Transfer to a wire rack to cool completely, or eat warm for breakfast with coffee!