Heat the olive oil in a large skillet over medium heat. Add the sausages in a single layer and cook for approximately 6–8 minutes, turning regularly until browned on several sides. They do not need to be completely cooked at this stage because they will finish cooking in the sauce. Transfer them to a plate and set aside, leaving the flavorful browned bits in the pan.

Add the sliced onion to the same pan and cook for 3–4 minutes until softened and lightly golden. If you are using carrot, add it now and cook for another 2 minutes. Stir in the minced garlic and cook for about 30 seconds, taking care not to burn it. These vegetables create a flavorful foundation for the sauce and help balance the richness of the sausages.

Stir the tomato paste, curry powder, and smoked paprika into the softened vegetables. Cook for approximately one minute, stirring continuously so the spices become fragrant. Add the Worcestershire sauce, ketchup, mustard, and optional brown sugar. Mixing these ingredients before adding the liquids helps distribute the seasonings evenly throughout the devilled sausages recipe.

Pour in the stock and tomato passata, stirring well to loosen any browned pieces from the bottom of the pan. Bring the mixture to a gentle simmer and taste the sauce before adding salt and pepper. If it tastes too sharp, a small amount of brown sugar can balance the acidity. If you prefer more heat, add a pinch of chili flakes or a little extra paprika.

Return the browned sausages to the pan, turning them so they are coated in the sauce. Reduce the heat to low, cover with a lid, and simmer gently for approximately 15–20 minutes, or until the sausages are cooked through. Stir occasionally and add a splash of stock or water if the sauce becomes too thick. Check the internal temperature using a food thermometer, following the safe temperature guidance for the type of meat used.

Remove the lid and simmer uncovered for a few minutes if the sauce needs to reduce. For a thicker gravy, stir in the cornstarch slurry and cook until the sauce thickens. Taste once more and adjust the seasoning. Garnish with chopped parsley and serve the hot sausages with mashed potatoes, rice, or your favorite vegetables.