Buttermilk adds a subtle, creamy tang to the grits.
Bring water, whole milk, and salt to a boil in a medium saucepan over medium-high. Gradually whisk in uncooked grits; return to a boil. Reduce heat to medium-low, and simmer, stirring occasionally, until creamy and thickened, 25 to 30 minutes. Remove from heat, and stir in buttermilk and 2 Tbsp. butter.
Stir Parmesan cheese into warm grits. Toss shrimp with Creole seasoning. Cook ham in 2 Tbsp. butter in a small skillet over medium-high, stirring constantly, just until beginning to brown, about 3 minutes. Stir in shrimp and minced garlic; cook, stirring constantly, 2 minutes. Stir in scallions, chicken stock, and wine, and cook until shrimp just turn pink and liquid is reduced by about half, about 2 minutes. Serve shrimp mixture over warm grits.