Add cauliflower into a food processor and pulse until the florets break down into fine pieces. You want it to be smaller than the size than cauliflower rice, about the size of regular grits and it's okay if it clumps together. This step might be easier done in two batches, depending on the size of your food processor.
Add 1 Tablespoon butter to a medium saucepan over medium heat. Transfer to a medium saucepan, pulse the remaining cauliflower and add that to the pan too. Add milk, 1 tablespoon of the butter, 1/2 teaspoon salt and several grinds of pepper and bring to a simmer over medium-high heat. Simmer, stirring frequently, until the mixture is soft and smooth and looks like grits, about 10 minutes. Remove from the heat, stir in the Parmesan and taste. Add more salt and pepper if you'd like. Cover and keep warm.
Melt the remaining 1 tablespoon of butter to a large skillet over medium-high heat. Add the shrimp, blackened seasoning and toss until the shrimp are pink and just cooked through, about 4 to 5 minutes. Remove from the heat, add the parsley, lemon juice and 1 tablespoon water and stir to coat the shrimp with the sauce. Season with salt and pepper.
Divide the cauliflower grits among shallow bowls, top with the shrimp and garnish with fresh parsley. Serve immediately.