* To substitute for buttermilk, use 2 tablespoons plus 1 1/2 teaspoons vinegar or lemon juice plus milk to make 2 1/2 cups.
To date, muffin pans have not been manufactured with an absolutely standard size. The cup size of older muffins pans tends to be larger than more recently manufactured pans. Both old and new are likely to yield smaller muffins than the mega-sized treats found in many bakeries.
Smaller muffin pans and those with a dark metal finish will require less baking time. Fill the muffin cups 2/3 to 3/4 full with batter. To check for doneness, insert a toothpick into the center of the muffin. If the toothpick comes out clean, the muffin is done.