Add 4 cups water and 2 teaspoons salt to a medium saucepan. Bring to a boil, then add the grits and reduce to a simmer. Cover and cook, stirring occasionally, until tender, about 30 minutes. Stir in the Cheddar, 3 tablespoons of the butter and the heavy cream, and keep warm.
While the grits cook, prepare the rest of the dish. Heat the oil in a large skillet set over medium heat. Add the tasso ham and cook, stirring occasionally, until starting to crisp, about 8 minutes. Add 1/2 teaspoon salt and the cracked pepper. Using a slotted spoon, remove the ham to a paper-towel-lined plate. In the same skillet set over medium-high heat, add 2 tablespoons of the butter and the shrimp. Cook, turning once, until bright pink, about 2 minutes. Using a slotted spoon, transfer the shrimp to a plate.
In the same skillet, reduce the heat to medium, then add the bell peppers, garlic, jalapenos and onions, and cook until the vegetables just starting to brown. Add the tomatoes and cook until they start to break down. Increase the heat to high, then add the stock and Creole seasoning. Scrape the brown bits from the bottom of the skillet with a wooden spoon. Cook until the stock reduces by half, 3 minutes. Return the shrimp and ham to the skillet along with the lemon juice and the remaining 2 tablespoons butter. Cook, stirring frequently, until the sauce thickens, about 1 minute. Divide the grits among four bowls and top each with some shrimp and sauce. Garnish with scallions to serve.