Preparation - Use a food processor to make cornflake crumbs. Pour crumbs in a shallow dish. Set aside. Mix together - mayonnaise, mustard, egg yolk and seasonings. Gently stir in crab meat. Form crab meat mixture, about 1/4 cup at a time, into small cakes. Coat each crab cake with cornflake crumbs. Place on a wax paper covered plate. Cover with plastic wrap and refrigerate about 2 hours. Place crab cakes on a baking sheet that has been sprayed with non-stick cooking spray. Top each one with about 1/2 tsp. butter. Bake in preheated 400º oven for 15 minutes, or until a golden brown color.