Preheat oven to 400℉ (200℃). Grease or line a muffin tin with paper liners.
In a medium bowl mix the 2 cups of Heritage Flakes cereal with the milk. Let stand for 5-10 minutes until the cereal softens.
Mix the wet ingredients: Add the egg, oil, brown sugar or honey, and vanilla extract to the softened cereal mixture. Beat well to combine.
Add Dry Ingredients: Stir in the flour, baking powder, salt, and cinnamon (if using). Mix just until combined. Do not over mix or the muffins will be tough.
Gently fold in any optional mix-ins (raisins, dried cranberries, or nuts). Fill muffin cups 3/4 full.
Bake for 18-22 minutes, or until a toothpick inserted comes out clean and the tops spring back when lightly touched.
Cool: Let muffins cool in the tin a few minutes, then transfer to a cooling rack.