Make the batter in advance, ladle into a sealable plastic container, and refrigerate up to two weeks. This is a great base for all sorts of add-ins. Try shredded carrot, raisins, dried cranberries or pineapple.
Mix cereal and wheat bran in a large bowl. Add boiling water and stir well.
Whisk together flour, baking soda, salt, cinnamon and nutmeg in a medium bowl.
Preheat oven to 375F. Coat muffin cups with cooking spray.
Add 1 cup buttermilk to bran mixture; stir well with a whisk. Add remaining buttermilk, egg substitute, granulated sugar, brown sugar, oil and vanilla, stirring until smooth.
Add flour mixture; stir until a thick batter forms. Stir in raisins.
Fill each muffin cup two-thirds full. Bake about 15-20 minutes, until puffed and lightly browned.