Step 1Stir together the brown sugar, flour, cinnamon and butter just until crumbly; do not overmix. Stir in the chopped walnuts. Cover and set aside.
Step 1Toast the nuts in a dry skillet over medium heat until lightly browned, 6 to 8 minutes. Chop them and set aside.
Step 2Heat the oven to 350 degrees. Grease 4 (8x3 3/4-inch) disposable aluminum loaf pans; sprinkle them with the ground nuts and set them aside.
Step 3In a large mixing bowl, blend the sugar, flour, baking soda and salt. Add the butter and blend until crumbly. With a rubber spatula, add the chopped walnuts and mix well.
Step 4Beat together the bananas, eggs and milk. Pour the banana mixture into the flour mixture all at once. Stir gently just until all the dry ingredients are moistened; do not overstir. Spoon the batter into the loaf pans. Sprinkle each loaf with Streusel Topping.
Step 5Bake until a toothpick inserted in the center comes out clean and the loaves come away from the sides of the pans, 45 minutes.