In a large skillet over medium heat, melt 3 tablespoons of butter. Add the diced onion and cook until softened, about 5 minutes. Add the flour and cook for another minute, stirring constantly.
Add the beef stock, Worcestershire sauce, thyme, rosemary, salt, and pepper. Bring to a boil, then reduce the heat and simmer until the gravy has thickened, about 10 minutes.
Meanwhile, cook the sausages in a separate skillet over medium-high heat until lightly browned and cooked through, about 10 minutes. Set aside.
Add the potatoes to a pot of boiling water and cook until tender, about 10 minutes. Drain and return to the pot. Add the milk, butter, and salt and pepper to taste. Mash until smooth.
To serve, spoon the mashed potatoes onto a plate or bowl. Top with sausages and onion gravy.
Interesting Facts
Bangers and Mash is a traditional British dish that has been around since the 19th century.
The name “Bangers” refers to the way the sausages would make a loud popping sound when cooked in a hot pan.
Bangers and Mash is often served with peas or other vegetables.