Nut Crunch Muffins

I have this recipe in my card collection from Great American Home Baking

Makes 1 dozen muffins

2 ½ cups all-purpose flour
½ cup coarsely chopped pecans, walnuts, or hazelnuts (about 2 ounces)
1/3 cup firmly packed light brown sugar
1/3 cup granulated sugar
2 teaspoons baking powder
1 teaspoon baking soda
1/8 teaspoon salt
1 cup buttermilk
2/3 cup vegetable oil
1 teaspoon vanilla extract
1 large egg

Topping
1/3 cup firmly packed light brown sugar
2 tablespoons all-purpose flour
½ teaspoon ground cinnamon
2 tablespoons chilled butter, cut into small pieces
½ cup coarsely chopped pecans, walnuts, or hazelnuts (about 2 ounces)

1. Preheat oven to 400F. Grease 12 standard size muffin-pan cups or line with paper liners.
2. Mix together flour, nuts, brown sugar, baking powder, baking soda, and salt.
3. Mix together buttermilk, oil, vanilla, and egg.
4. Make a well in the center of flour mixture. Add buttermilk mixture all at once to well, tossing with a fork until dry ingredients are just moistened. (Do not overmix.)
5. Spoon batter into prepared pan, filling cups two-thirds full.
6. To prepare topping, in a medium bowl, mix together brown sugar, flour, and cinnamon.
7. Using a pastry blender or 2 knives, cut butter into flour mixture until coarse crumbs form. Stir in nuts. Sprinkle topping evenly over batter.
8. Bake muffins for 10 minutes. Lower oven temperature to 350 F.
9. Bake muffins until tops are golden, 12 minutes more.
10. Transfer pan to a wire rack to cool for 5 minutes. Turn muffins out onto rack to cool completely.

Baking Tips:
Substitute soured milk for the buttermilk. To prepare soured milk, bring milk to room temperature. Mix together 1 tablespoon white vinegar or lemon juice with milk to make 1 cup. Let mixture stand until curdled, about 10 minutes.