Preheat oven to 350º.
Combine milk, 2 cups water, and 1/2 teaspoon salt in a medium saucepan over medium-high heat; bring to a boil. Add grits, stirring with a whisk. Cover, reduce heat, and cook 8 minutes or until liquid is absorbed. Remove from heat; stir in 1/4 teaspoon salt, cheese, and pepper. Cool 5 minutes.
Place remaining 1/4 teaspoon salt and egg whites in a large bowl. Beat egg whites with a mixer at high speed until stiff peaks form (do not overbeat). Gently fold grits mixture and chives into egg whites; spoon mixture into a 13 x 9-inch baking dish coated with cooking spray. Brush evenly with butter. Bake at 350° for 40 minutes or until browned. Let stand 10 minutes before serving.