Preheat the oven to 400 degrees F. In a food processor, finely grind 1 1/2 cups of the cereal. Transfer the mixture to a bowl with remaining 3/4 cup of cereal, blueberries, flour, whole-wheat flour, sugar, baking soda, and salt. Set aside.
Combine butter, eggs, yogurt, honey, and vanilla. Stir together wet and dry ingredients until just combined.
Line muffin tin with baking cups. Fill each just more than halfway. Sprinkle generously with sugar crystals, if desired. Bake until a toothpick inserted into the center comes out clean, about 18 minutes. Remove from tin and allow to cool slightly.