01 - Place the peeled and chunked potatoes into a large pot. Cover with salted water and bring to a rolling boil. Cook for 15 to 20 minutes, or until the potatoes are fork-tender. Drain thoroughly and return the potatoes to the pot. Add the milk, butter, salt, and freshly ground black pepper. Mash until smooth and creamy. Cover to keep warm while you proceed with the next steps.
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 deeply browned and cooked through. Transfer the cooked sausages to a plate and keep them warm.
03 - Using the same skillet (do not clean it), 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 occasionally, for 10 to 12 minutes, until the onions are beautifully soft and golden brown.
04 - Sprinkle the 2 tablespoons of all-purpose flour evenly over the softened onions. Stir continuously for 1 to 2 minutes, ensuring the flour is fully absorbed and cooks out slightly.
05 - Gradually pour in the 2 cups of halal beef or vegetable stock, stirring constantly to prevent lumps. Stir in the halal-certified Worcestershire sauce and Dijon mustard. Bring the gravy to a gentle simmer and cook for 5 to 7 minutes, stirring frequently, until it has thickened to your desired consistency. Season the gravy with salt and freshly ground black pepper to taste.
06 - Arrange the cooked halal sausages artfully on top of the creamy mashed potatoes. Generously spoon the rich onion gravy over both the sausages and potatoes. Serve immediately and enjoy this comforting British classic hot.