Satisfying, cheesy dips steal the show at any holiday gathering, and they're well-suited for teaching young cooks the basics of sauce-making and presentation.
Lightly oil or butter a small shallow casserole (about 1 1/2 quarts). Heat the oven to 375°.
Melt the butter in a medium-size skillet. Add the onion and garlic, and saute them over low heat for 5 minutes, stirring frequently. Add the Old Bay or other seafood seasoning and cook another 30 seconds, continuing to stir. Remove the skillet from the heat.
Using an electric mixer, blend the cream cheese, sour cream, and mayonnaise. Add the lemon juice, Worcestershire sauce, mustard, and milk, and blend the mixture again until it's smooth. With a spoon, stir in the crabmeat, half of the cheese, and the sauteed onion and garlic.
Transfer the dip to the prepared baking dish and smooth the top with a spoon. Sprinkle the remaining grated cheese over the top. Place the dish in the oven and bake until the top of the dip is bubbly, about 20 to 25 minutes. Serve warm with celery sticks, bell pepper strips, and toasted baguette slices. Serves 12 as an appetizer.