Lightly spoon flour into measuring cup; level off. In large bowl, combine flour, brown sugar, sugar, baking powder, baking soda and salt; blend well. In small bowl, combine buttermilk, oil vanilla and eggs; mix well.
Add liquid ingredients to dry ingredients; stir just until dry ingredients are moistened.
Cover tightly; refrigerate up to 5 days. (If desired, muffins can be baked immediately.)
To Bake, heat oven to 375º . Choose one of the flavor variations given below. Grease bottoms only of 6 muffin cups or line with paper baking cups. In small bowl, place 1 1/3 cups batter. Fold in flavor ingredients. Fill muffin cups 2/3 full. Bake at 375º
Raisin spice: Fold in 1/3 cup raisins, 1/2 tsp. cinnamon, 1/4 tsp. nutmeg, 1/4 tsp. allspice and 1/4 tsp. cloves.
Maple walnut: Fold in 1/3 cup chopped walnuts and 1/2 tsp. maple extract.
Pineapple coconut: Fold in 1/3 cup drained, crushed pineapple and 1/4 cup coconut.
Chocolate Chip: Fold in 1/3 cup miniature semi-sweet chocolate chips.
Mixed fruit: Fold in 1/3 cup chopped dried mixed fruit.
Cinnamon Topped: After baking, dip top of each muffin in melted butter, then a mixture of 2 tablespoons sugar, 1/4 tsp. cinnamon and 1/3 tsp. nutmeg.