Preheat oven to 375°.
Lightly coat an 11 x 7-inch baking dish with cooking spray, and dust with breadcrumbs. Set aside.
Heat a large nonstick skillet over medium heat. Coat pan with cooking spray. Add garlic; cook 20 seconds, stirring constantly. Add spinach; cook 3 minutes or until spinach wilts, stirring occasionally. Remove from heat; cool slightly. Place spinach mixture on several layers of heavy-duty paper towels, and squeeze until barely moist. Place spinach mixture in a blender. Add milk and cornstarch; process until smooth. Add cheese, salt, pepper, and nutmeg; pulse until well blended. Pour into a large bowl.
Place egg whites and egg in a large bowl; beat with a mixer at high speed 5 minutes or until tripled in volume. Gently fold one-fourth of egg mixture into spinach mixture; gently fold in remaining egg mixture (mixture will seem slightly thin). Spoon spinach-egg mixture into prepared baking dish; smooth top with a spatula.
Bake at 375° for 35 minutes or until set in the center. Cool 5 minutes on a wire rack before serving.