Nutmeg Struesel Muffins

1-1/3 c all-purpose flour
1 c firmly packed brown sugar
½ c cold butter
Muffin Ingredients:
2/3 c all-purpose flour
2/3 c buttermilk
1 egg
1-1/2 tsp baking powder
1-1/2 tsp ground nutmeg
½ tsp baking soda
½ tsp salt

Heat oven to 400°F. Combine 1 1/3 cups flour and brown sugar in large bowl; cut in butter with pastry blender or fork until mixture resembles coarse crumbs. Reserve 1/2 cup for streusel topping. Add all muffin ingredients to remaining streusel mixture in same bowl; stir just until moistened. Spoon batter into greased or paper-lined 12-cup muffin pan. Sprinkle with reserved streusel topping. Bake for 18 to 22 minutes or until lightly browned. Let stand 5 minutes; remove from pan.