Preheat the oven to 325. Grease a 9 x 5 loaf pan and line with parchment, and set aside.
In a large bowl or the bowl of a stand mixer, cream together the sugar and butter until light and fluffy. Add the eggs, vanilla, and milk, and mix until smooth.
Add the flour, salt, baking soda, and baking powder, and mix until just combined. Fold in the mashed bananas and pour into the prepared loaf pan.
To make the streusel, whisk together the sugar, flour, and cinnamon. Smash in the butter using your fingers, until the mixture resembles damp sand. Sprinkle the streusel mixture over the top of the loaf. Bake 60-70 minutes, or until golden brown on top and a toothpick inserted into the center comes out clean. Let cool before serving.