Cover grits with water, bring to a low boil then simmer until water is almost absorbed. Add milk and cook until creamy, stirring, about 30 minutes.

Meanwhile, in a medium skillet, heat the vegetable oil and cook the green pepper, celery, onion, and garlic, stirring, until lightly browned. Stir in 2 tablespoons butter until melted, then stir in flour to make a light roux. Stir in tomato and shellfish stock and once combined, add shrimp and spices. Lightly poach shrimp for 2 to 3 minutes.

Once grits are cooked and creamy, stir in cream cheese, cheddar cheese, and sour cream until melted, then fold in pimentos and remaining 2 tablespoons butter.

Season shrimp with lemon juice, hot sauce (if using), salt and pepper. 

Spoon grits into a shallow bowl, top with shrimp and sauce, and garnish with scallions.