Preheat the oven to 350°F.

Use 2 tablespoons of butter to grease 8 straight-sided baking cups (or a 1½-quart soufflé dish).

Place the bread and the butter pieces in a large bowl. In a small saucepan, bring the milk to just below boiling and pour all but 2 tablespoons over the bread. Do not stir; set aside for at least 30 minutes while the milk soaks into the bread.

In a small bowl, combine the egg yolks, garlic, Parmesan, salt and the remaining 2 tablespoons of milk. Gently fold this mixture into the soaked bread.

Whip the egg whites to soft, not dry, peaks and fold them into the bread mixture. Divide the custard equally among the cups and bake for about 50 minutes (1 hour, 5 minutes in a soufflé dish), or until the custard is puffed, golden brown, and set in the center. Cool for 15 minutes (they will fall as they cool) and unmold.

Place the custards on a serving plate and surround them with the slices of prosciutto.

Makes 8 servings.