Peel limes with a sharp paring knife or a vegetable peeler, being careful not to cut into the white pith. Combine lime peel and water to cover in a small saucepan; bring to a boil, then reduce heat and simmer 5 minutes. Drain and set aside.
Juice limes, discarding membrane and pith. Process lime juice, peel, sugar, eggs, and milk 5 minutes in a blender, stopping to scrape down sides. Pour mixture through a wire-mesh strainer into six (4-ounce) ovenproof containers. Place in a large baking pan. Add hot water to pan to depth of 1 inch.
Bake at 275 degrees F until a knife inserted in the center comes out clean, about 30 minutes. Garnish if desired.
Per serving: 145 calories, 5 grams protein, 24 grams carbohydrate, 4 grams fat, 140 milligrams cholesterol, 55 milligrams sodium, trace of fiber.