• Preheat oven to 375℉
• In an ovenproof frying pan, heat the olive oil and cook the sausages over a medium-high heat for about 8 minutes, turning them util browned on all sides.
• Transfer to a plate and add the butter to the pan. Scatter the onions, stirring them into the butter. Add the thyme sprig and sugar. Stir to combine.
• Add the sausages on top and pour any juices accumulated on the plate. Roast for about 20 minutes, turning the sausages halfway through.

Make the mash

• Put the chopped potatoes into a saucepan of cold salted water and bring to a boil. Once boiling, reduce the heat and simmer for about 10-12 minutes or until just cooked all the way through. Test by inserting a sharp knife into the potato. It should slide in easily. Drain in a colander
• Add the milk to the pan and bring to a simmer, then add the potatoes and mash coarsely with a potato masher. Add the butter a little at a time, stirring to incorporate with a wooden spoon. Turn off the heat and keep warm.

Make the onion gravy

• When the sausages are cooked, remove from the oven and remove the sausages to a plate. Keep them warm.
• Put the pan back on the heat and give the roasted onions a stir, they should be sticky and caramelized around the edges. Stir in the flour and cook for about 1 minute. Pour in the vinegar and simmer for 30 seconds then pour in the red wine and soy sauce. Stir until it has thickened. Add the beef stock, stirring constantly as it continues to thicken.

Serve the Bangers and Mash

• Scoop a mound of mash onto the middle of each plate, then top with the sausages and the onion gravy.