Preheat oven to 350°F and line a bottom of a 9 inch baking pan with parchment paper, and grease the sizes and the dollops on the bottom to keep the parchment paper in place when adding the batter.
In a small bowl, combine the flour, brown sugar, cinnamon and cold butter for the streusel. Add the walnuts once you sprinkle the streusel on each layer. Set in the refrigerator until ready to assemble cake.
In a mixer, cream together butter and sugar. Add eggs to the mixture, one at a time, and beating well after each addition.
In a separate bowl, sift together the flour, baking soda, baking powder and salt. Mash the bananas in a measure cup or small bowl, using a fork stir in maple syrup and vanilla.
Add the dry ingredients to the creamed mixture alternately with the banana mixture, by starting with flour and end with flour. Mix until combined, but don’t over mix.
Scoop 1/2 of the batter to the baking pan and using a spatula and knife to spread the batter evenly. Sprinkle the streusel evenly over the batter and half of the walnuts. Add the remaining batter and spreading evenly, then add the remaining streusel and walnuts on the top. You can always add extra chopped walnuts.
Bake for 40-45 minutes, until a tooth pick inserted in the middle of the cake comes out clean.
When sufficiently cool, turn the cake out onto your serving platter. Stir together the glaze ingredients, and drizzle the glaze on top of the cake, allowing it to cascade down the sides or drizzle on each individual slice.
