Prepare coating: Spread crushed cornflakes in a shallow pan.
Mix ingredients: Whisk mayonnaise, mustard, Old Bay, cayenne, and egg yolk, then fold in crab meat. Season with salt and pepper.
Shape the cakes: Divide mixture into 10 portions and shape into slightly flattened cakes.
Coat with cornflakes: Press each cake into crushed cornflakes until fully covered.
Chill: Cover and refrigerate for 2-4 hours to firm up.
Preheat oven: Set to 400°F (200°C).
Bake: Place crab cakes on a greased baking sheet, top each with butter, and bake for 15 minutes until golden brown.
Serve hot: Enjoy with a dipping sauce or fresh lemon wedges!