Preheat oven to 350 degrees. Mix 2 cups of the flour and brown sugar in medium bowl. Cut in butter until mixture forms coarse crumbs. Remove and reserve 3/4 cup of this mixture for topping.
Add remaining 1 cup flour and remaining dry ingredients to mixture in bowl. Add buttermilk and eggs, stirring just until moistened.
Spoon batter into well greased muffing cups or paper liners in muffing cups, filling each about half-full. Sprinkle each muffin with 1 1/2 teaspoons of reserved topping. Bake until wooden pick inserted in center comes out clean-about 20 minutes. Makes 36 mini-muffins or 1 1/2 dozen mini-muffins and 1 dozen regular muffins, or 2 dozen regular muffins.
Note: Muffins can be frozen. Remove from freezer 1 hour before serving. Heat in foil at 275 degrees for 15 minutes.