HEAT oven to 350°F. HEAT milk in small saucepan until very hot. Milk should be steaming but not bubbling. Meanwhile BEAT eggs, sugar, vanilla and salt in medium bowl until blended but not foamy; slowly stir in hot milk.
PLACE six lightly greased 6-oz. custard cups in baking pan large enough to hold cups without touching each other or sides of pan. POUR egg mixture into cups, dividing evenly. SPRINKLE with nutmeg, if desired.
PLACE pan on rack in center of 350°F oven; pour very hot water into pan to within 1/2 inch of top of cups. BAKE until knife inserted near center comes out clean, 25 to 30 minutes; center will still be soft. REMOVE cups from hot-water bath at once; cool on wire rack 5 to 10 minutes. SERVE hot or refrigerate until cold.
One-dish custard: Recipe can be baked in lightly greased 1-1/2-quart soufflé or baking dish. Pour hot water to within 1 inch of top of dish. Increase baking time to 35 to 40 minutes.
No-mess pouring: Make custard in a bowl with a pouring lip, or transfer it to a large glass measure, to make filling custard cups easier and neater.
For perfectly smooth custard: Strain it through a sieve to remove any tough egg strands.
Don't skip the hot-water bath. A hot-water bath, or bain-marie, insulates the custard from the direct heat of the oven and promotes even cooking so the edges don't overcook before the center is done. Very hot tap water will do.
When is it done? Baked custard should be removed from the oven (and water bath) before the center is completely set. The center will jiggle slightly when dish or cup is gently shaken. Custard will continue to "cook" after it's removed and center will firm up quickly. Overbaked custard may curdle. The knife test: Test for doneness with a thinbladed knife. Insert knife about 1 inch from the center of a one-dish custard; midway between center and edge of cups. If knife is clean when pulled out, the custard is done. If any custard clings to the blade, bake a few minutes longer and test again.