Preheat the oven to 180°C/350°F/Gas Mark 5
First make the burgers, heat 1 tablespoon of the rapeseed oil in a small saucepan, add the onion and stir well. Cover and cook for 5 minutes, until the onion has softened, but do not allow to brown. Remove to a mixing bowl and leave to cool. Once cool, mix in the sausage meat, chopped sage and a little freshly ground black pepper. Mix well and form the mixture into 4 burger-shaped patties.
For the sweet potato chips, drizzle rapeseed oil over the sweet potatoes in a large bowl so that they are all well coated. Season with black pepper and place in a roasting tin. Roast in the preheated oven for 30 – 35 minutes until cooked through and golden brown around the edges. Season with sea salt and keep warm.
For the spiced apple wedges, melt the butter in a small frying pan. Add the apple wedges, spices, sugar, white wine vinegar and stir over a low heat until the apples are caramelised and soft, around 5 minutes.
Brush the sausage burgers with the remaining rapeseed oil and cook on a hot barbecue for 5 – 10 minutes on each side, until cooked through. Serve with the apple wedges and sweet potato chips.