* To substitute for buttermilk, use 1 1/2 teaspoons vinegar or lemon juice plus milk to make 1/2 cup.
** If necessary to bake muffins in batches, remaining batter can be refrigerated and baked as soon as possible.
Originally, buttermilk was the liquid left after butter was churned. Today, it's made commercially by adding special bacteria cultures to low-fat or nonfat milk. Despite buttermilk's thick consistency and rich flavor, it is a low-fat or nonfat product. In baking, it provides tang and tenderness.
Stir 1/2 cup finely chopped walnuts into the batter.
Dress up the muffins with a drizzle of icing made with powdered sugar and lemon juice.