Preheat the oven to 375℃/190℃. Grease 12 muffin cups, or line with muffin paper.
In a large bowl, combine 180 g flour, ⅛ teaspoon salt, 1 teaspoon baking soda and 1 teaspoon baking powder.
In a separate large bowl, blend 3 over ripe bananas, 1 teaspoon vanilla, 150 g sugar, 80 g melted butter and 1 medium egg.
Stir the banana mixture into the flour mixture until it is moistened and there are no lumps of flour (take care not to over-mix it).
Spoon the mixture into the muffin tray.
For the streusel topping
In a small bowl, combine 70 g light brown sugar, 2 tablespoons flour and ¼ teaspoon ground cinnamon
Add 1 tablespoon softened butter and mix well. Sprinkle over the muffins.
Bake in the preheated oven for 15 minutes. Allow to cool on a wire rack.
Notes
Freeze ripe bananas so you always have some on hand. They can be frozen with the skin on or peeled and transferred to a zip-loc bag. Bring to room temperature before using.
Stir the mixture by hand to avoid over-mixing, this avoids a dense muffin.
Stir ½ cup chocolate chips into the batter before baking.
Store muffins in an airtight container and leave in a cool place.