Step 1Heat the oven to 350 degrees. Generously butter a 13x9-inch baking dish.
Step 2Place the hot grits in a mixing bowl and stir in the cheese, butter, mace, salt and cayenne pepper. Cool slightly.
Step 3In a small bowl, lightly beat the egg yolks. Stir a little of the grits mixture into the yolks to heat them slightly, then add to the grits mixture and combine thoroughly. Let cool to room temperature.
Step 4Beat the egg whites until soft peaks form and fold them into the cheese grits. Pour into the dish and bake until the souffle is puffed and lightly browned, 40 to 45 minutes.