Based on a recipe from Bruce Weinstein's & Mark Scarbrough's book, "The Ultimate Peanut Butter Book". I'm wild about peanut butter! The authors say, "Muffin tins don't come in standardized sizes. This recipe was developed for a tin in which each indentation holds about 1/3 cup batter. If yours holds more, increase the baking time by a few minutes; if less, decrease accordingly." These may also be customized, per the authors, by stirring in "2/3 cup dried cranberries, raisins, or semisweet chocolate chips in with the flour. Or add 1 teaspoon ground cinnamon with the vanilla."