Melt the butter and add the shrimp and cook together for 2 minutes. Add to the creole sauce. Simmer for 5 minutes, and serve with boiled rice. For the sauce: Cook the tomatoes, pepper, onion and mushrooms for 10 minutes. Add the stock and ham and cook 2 minutes longer. Thicken with the flour lightly creamed with the butter and stir until thick and smooth. Serves 6.