Sausage and Mash Pie with Onion Gravy

Heat the sunflower oil in a large frying pan over medium-high heat. Add the sausages and cook for 10-12 minutes, turning often, until browned all over. Transfer them to a plate. Add the butter to the same pan, then stir in the sliced onions and sugar. Cook for 8-10 minutes, stirring occasionally, until the onions are soft and golden.

Sprinkle the flour over the onions and stir until no dry patches remain. Mix in the tomato puree and cook for 1 minute. Add the red wine vinegar, then gradually pour in the beef stock while stirring. Bring to a boil, reduce to a simmer, and add any sausage juices from the plate. Slice the sausages thickly, return them to the pan, and simmer for 5 minutes until the gravy is glossy and lightly thickened. Spoon the filling into a baking dish.

Put the potatoes in a large saucepan of cold salted water. Bring to a boil, then reduce the heat and simmer for 10-12 minutes, or until a knife slides through easily. Drain well and let the potatoes steam-dry for 1 minute.

Warm the milk in the empty pan until just steaming. Add the drained potatoes and mash until smooth, adding seasoning to taste. Heat the oven to 200C/180C fan/gas 6.