Pour oil into a large, heavy-bottomed soup pot and when it is smoking hot, gradually whisk in the flour, forming a 'roux'. Continue stirring the roux, whisking constantly until it begins to deepen in colour. Be careful it is very hot! When the roux is deep golden brown add the onions, green peppers and celery. Cook for a few minutes until they have softened. Add the chicken broth and stir until thickened. Add the sausages, shrimp, tomatoes, okra and spice blend. Taste, then season with salt and pepper as desired. Add more Louisiana spice blend if you like. Simmer until the sausages and shrimp are cooked through.