Add diced tomatoes to a saucepan, season with salt and pepper. Simmer for 12-15 mins, creating a thick paste with some liquid.
In a cast iron skillet, melt bacon grease or butter. Add onion, garlic, and thyme. Stir for 5 mins until onion is translucent. Add flour, stir for 1-2 mins until golden.
Pour chicken broth into the skillet, mix until smooth, and the gravy thickens. Add stewed tomatoes. Adjust consistency with water or broth if needed.
Pour in heavy cream, stir well. Taste the gravy, adjust salt and pepper to taste. The gravy should be thick enough to spread over biscuits, rice, or mashed potatoes.
Serve the flavorful tomato gravy over hot buttermilk biscuits, rice, or mashed potatoes. Enjoy your delicious homemade tomato gravy!