Heat oven to 400°F. In a food processor, finely grind half the cereal. Add raisins (or the other dried fruit you are using) and blend until finely chopped. Transfer 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. Bake until muffins spring back when touched, 15 to 18 min. Remove from the tin and allow to cool slightly.