You can substitute 2/3 cup of the flour for ground nuts like almonds or hazelnuts for extra flavour.
1-2/3 cups of butter (cubed to pea size and chilled)
1-2/3 cups all purpose flour, sifted
2/3 cup brown sugar
2/3 cups white sugar
Additional Optional ingredients
1/2-2/3 cup chopped pecans or walnuts
1/2-2/3 cup rolled oats
1 tbsp ground cinnamon
Combine sifted flour, brown sugar, and white sugar in a large bowl. (if adding ground nuts or spices, add them at this stage.)
Add pea-size cubes of chilled butter, and cut into flour sugar mix by rubbing it between your fingertips until the mixture resembles coarse crumbs. (The butter can also be cut into the mixture with a fork or pastry blender.)
Toss chopped nuts and/or oats into streusel mix, if desired.
Sprinkle streusel topping over muffins, fruit crumbles, coffee cakes or pies just before baking.
Leftover streusel can be frozen for later use. Use straight from frozen.