Melt bacon fat and sauté the onion until translucent. Add the sausage and cook until the sausage is beginning to brown a little at the edges. Add the flour and stir for a few minutes while the raw flour taste cooks off.
Add the garlic and tomatoes. Cook for a couple of minutes to let the tomato juices reduce a little. Add wine, basil, salt and pepper, and pepper flakes. Turn the heat to low and simmer for 20 minutes. While the sauce is simmering, make grits using the recipe below and keep warm.
When the grits are done and the sauce has simmered, turn the sauce to medium heat. Add the shrimp, and cook just until shrimp are uniformly pink. Turn off the heat. Ladle shrimp sauce over grits and serve immediately.