For the cakes, beat butter with sugar for 3 minutes. Add eggs and vanilla, beat until combined. Add mashed bananas and beat until blended. Add flour, baking soda, baking powder and salt until combined. Beat in nuts and skim milk.
Pour batter into two 9-inch round cake pans that have been greased generously.
In a small bowl, mix streusel topping ingredients together. I use my hands to break up the butter and mix it with the other ingredients. Mix until it forms crumbs. Divide topping evenly between the two cakes, sprinkling on the top. Bake in a 350 degree oven for 25 minutes. Remove and cool on a wire rack for 10 minutes. Remove from pans and cool on rack completely before adding glaze.
For the glaze, beat powdered sugar with maple syrup until desired consistency. Drizzle over cakes. Store in airtight container.
Notes
The more maple syrup you add to the glaze, the thinner it will be. If it's too thick to pour over your cakes, add more syrup a little at a time.
Cool the cakes in the pans for about 10 minutes to make them easier to remove. Then, turn them out of their pans to finish cooling on a wire rack.
Store the cakes in an airtight container at room temperature until ready to serve.