01 - Place the peeled and chunked potatoes in a large pot. Cover with cold, salted water and bring to a boil. Cook for 15 to 20 minutes, or until the potatoes are very tender when pierced with a fork. Drain thoroughly and return the hot potatoes to the pot. Add milk, butter, salt, and pepper. Mash until smooth and creamy. Cover to keep warm while you prepare the other components.
02 - While the potatoes are cooking, heat 1 tablespoon of vegetable oil in a large skillet over medium heat. Add the halal sausages and cook, turning them occasionally, for 15 to 20 minutes, or until they are well-browned and cooked through. Transfer the cooked sausages to a plate and cover to keep warm.
03 - Using the same skillet (do not clean it, as the sausage drippings add flavor), add 2 tablespoons of unsalted butter and 1 tablespoon of vegetable oil. Add the thinly sliced onions along with a pinch of salt. Cook over medium-low heat, stirring periodically, for 10 to 12 minutes, or until the onions are soft, caramelized, and golden brown.
04 - Sprinkle 2 tablespoons of all-purpose flour over the caramelized onions and stir continuously for 1 to 2 minutes, ensuring the flour is fully absorbed and cooks slightly to remove any raw taste.
05 - Gradually pour in the 2 cups of halal beef or vegetable stock while stirring constantly to prevent lumps. Add the halal-certified Worcestershire sauce and Dijon mustard. Bring the mixture to a simmer and cook for 5 to 7 minutes, stirring frequently, until the gravy thickens to your desired consistency. Taste and adjust seasoning with salt and pepper.
06 - To serve, spoon a generous portion of creamy mashed potatoes onto each plate. Top with the cooked sausages, then generously ladle the rich onion gravy over both the sausages and potatoes. Serve immediately and enjoy hot.