To pickle the onions, put the onions in a small non-reactive bowl. Pour the vinegar into a saucepan and stir in the sugar and bay. Bring to a simmer, then pour this over the onions. Cover and chill for at least 1 hr 30 mins, or overnight.

For the lager onions, heat the oil in a saucepan over a medium heat and cook the onion, garlic, thyme and bay for 5-8 mins, stirring to prevent sticking, until golden and caramelised. Add the sugar and vinegar, cook for 2 mins more, then pour in the lager. Simmer for 15 mins over a low heat, stirring occasionally until the liquid has reduced to a sticky, caramelised consistency. Season, then remove from the heat and decant into a container until needed. Will keep chilled for a few days.

Combine all the ingredients for the monkey gland sauce in a bowl or jug. You can transfer it into a squeezy bottle or piping bag. Will keep chilled for a few days.

Prepare your barbecue (or braai). For best results, let the fire and coals or wood settle until you have white dust on the outside of the coals or wood. The boerewors is best cooked over a hot, indirect heat for 12-15 mins, depending on the thickness of the sausage, until cooked through.

To serve, split the brioche buns, spread the lager onions over the base, then put a sausage-sized slice of the boerewors on top. Drizzle over the monkey gland sauce and squeeze over the American mustard, if using. Finish with a spoonful of the pickled onions.