Preheat oven to 350 degrees F. In a small saucepan, combine 1/2 c milk and the mint-chocolate chips. Cook over low heat, stirring constantly, until chips are melted and mixture is smooth. Set aside. In a large bowl, combine remaining 1 c of milk, condensed milk, and eggs; beat until well blended. Add chocolate mixture; beat well. Pour into a 1-quart casserole. Fill a 13 x 9 x 2-inch baking pan with 4 cups of water. Place casserole in baking pan. Bake at 350 degrees F. for 50 to 55 minutes. Serve warm or cool completely.