Combine 3/4 cup of the flour and sugar in a medium bowl. Cut in the butter with a pastry blender or two forks used scissor style until mixture resembles coarse crumbs. Set aside 1/2 cup of the mixture for the topping.
Add the remaining 1 cup of flour, baking powder,baking soda, cinnamon, and nutmeg. Mix well. Add eggs and banana, mix just until incorporated, careful not to over mix.
Toss the blueberries with 1 teaspoon of flour. Stir them in with the walnuts. Pour into prepared pan. Sprinkle reserved topping evenly over top.