In a large pot, boil the diced potatoes until fork-tender. Drain and mash with the milk, butter, salt, and black pepper until smooth and creamy.
In a skillet, heat the vegetable oil over medium heat. Add the sausages and cook until browned on all sides and cooked through.
Meanwhile, in another skillet, caramelize the sliced onions in a bit of oil until golden brown.
Remove the sausages from the skillet and set aside. In the same skillet, sprinkle flour over the caramelized onions and stir to create a roux.
Gradually whisk in the broth, making sure there are no lumps. Add Worcestershire sauce and simmer until the gravy thickens.
Serve the sausages on a bed of creamy mashed potatoes, generously ladled with the rich onion gravy.
Garnish with fresh parsley and season with additional black pepper if desired.
