Bring 5 cups water to a boil in a medium saucepan over medium-high heat. Add the grits and a pinch of salt and cook, stirring, until just starting to thicken, about 5 minutes.
Add the milk and bring to boil, then adjust the heat to maintain a low simmer. Partially cover and cook, stirring every few minutes, until thick and creamy, 10 to 20 minutes.
Remove from the heat and stir in the butter and cheese (reserve a pinch for garnish) until melted. Season with salt and pepper.
Transfer to a serving bowl. Garnish with the scallions and the reserved cheese.
Recipe courtesy of Rev Run's Sunday Suppers