Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking dish.
In a medium bowl, whisk together 2 cups of flour, baking soda, and salt.
In a large bowl, cream together 1/2 cup of butter and 3/4 cup of brown sugar until light and fluffy. Beat in the eggs one at a time, then stir in the mashed bananas and vanilla. Stir in the flour mixture, just until incorporated. Pour batter into the prepared dish.
In another bowl, mix together 1/2 cup of brown sugar, 1/2 cup of flour, and cinnamon. Cut in 1/4 cup of butter until the mixture resembles coarse cornmeal. Sprinkle the topping over the batter.
Bake in the preheated oven for 45 to 50 minutes, or until a toothpick inserted into the center comes out clean.
For the glaze, in a small bowl, mix the powdered sugar and milk until smooth. Adjust the thickness with more milk or sugar as needed. Drizzle over the cake while it's still warm.