Make the Mashed Potatoes
Bring a pot of salted water to a boil. Add the potato cubes and cook until tender, about 15 minutes. Drain, then mash with butter, warm milk, salt, and pepper until creamy. Keep warm.
Cook the Sausages
In a large skillet, heat olive oil over medium heat. Add the sausages and cook until browned and cooked through, turning often for even color. Remove from the pan and keep warm.
Prepare the Onion Gravy
In the same skillet, melt butter and add sliced onions. Cook slowly for 8–10 minutes until golden and caramelized. Stir in the flour and cook for another minute.
Gradually pour in the broth while whisking to create a smooth sauce. Add Worcestershire sauce, mustard (if using), and season with salt and pepper. Simmer until thickened.
Assemble and Serve
Spoon mashed potatoes onto plates, place the sausages on top, and drizzle with the rich onion gravy. Sprinkle with chopped parsley for a fresh finish.
