In a medium mixing bowl stir together whole bran cereal and oat bran. Stir in the boiling water. Stir in milk, egg whites, and oil. Set aside.
In a small bowl stir together flour, brown sugar, baking powder, cinnamon, and salt. Add all at once to cereal mixture, stirring just until moistened.
Bake immediately or store batter in a tightly covered container in the refrigerator for up to 3 days.
To bake, spray 2-1/2-inch muffin cups with nonstick spray. Stir muffin batter and fill muffin cups two-thirds full. Bake in a 400 degree F. oven about 20 minutes or until a toothpick inserted near the center comes out clean. Remove from pans; serve warm. Makes 12 muffins.