Preheat the oven to 400 degrees F. In a food processor, finely grind half of the cereal. Add the raisins to the mixture, but do not grind them. Transfer the mixture to a bowl with remaining cereal, flour, whole-wheat flour, sugar, baking soda, and salt. Set aside.
Combine butter, eggs, yogurt, molasses, and vanilla. Stir together wet and dry ingredients until just combined. Do not over mix.
Line muffin tin with baking cups. Fill each just more than halfway. Sprinkle generously with sugar crystals, if desired (they add a good taste). Bake until muffins spring back when touched or when a toothpick inserted into the center comes out clean, about 18 minutes. Remove from tin and allow to cool slightly.