Wash and trim the ends off the asparagus. If the stalks are thin, just arrange them in your gratin dish. If the stalks are thick, you'll want to pre-cook them just a bit. Blanch them in boiling water for about a minute or so to tenderize it a bit. Bring water to a boil, add the asparagus, and start timing right then. Drain and arrange in your gratin dish.
Melt the butter in a saucepan, and whisk in the flour. Cook for just a minute, but don't let it brown. Then whisk in the milk and cream and blend well. Add the nutmeg, salt and pepper and continue heating until the sauce thickens, stirring or whisking constantly.
Take the sauce off the heat and stir in the cheeses until the they melt and the sauce is smooth.
Pour the sauce over the asparagus and bake for about 30 minutes, or until bubbling and beginning to brown. Toward the end of cooking, top the gratin with the breadcrumbs. Note: I top with the breadcrumbs about halfway through cooking so they don't brown too much.