For the apple relish, combine all the ingredients in a saucepan and stir over a low heat until the sugar dissolves. Increase the heat to medium and cook, stirring occasionally, for 20 minutes or until syrupy.
Remove from the heat and allow the relish to cool until ready to serve. The relish will keep in the fridge in an airtight jar for up to 3 weeks, so is perfect for making ahead.
For the burgers, combine the pork, garlic and shallots in a large bowl, season with salt and freshly ground pepper and mix until well combined. Using wet hands, form into 6 burgers and refrigerate for at least 30 minutes.
For the onion rings, heat the vegetable oil in a deep-fryer to 180°C. Double-dip the onion rings in buttermilk and the fine polenta or cornmeal. Deep-fry for 1-2 minutes or until golden. Drain on kitchen paper and season to taste.
Heat the olive oil in a large frying pan, add the burgers and cook over a medium-high heat for 4-5 minutes per side or until just cooked through.
Combine the cabbage and mayonnaise and season to taste. Toast the cut sides of the buns, top with the cabbage and place the burgers on top. Spoon over some apple relish, then sandwich together.
Serve immediately with the onion rings and some barbecue sauce on the side.
*All information included in this recipe has been provided by Chingford Fruit Ltd. This recipe was created by Reuben Riffel, head chef at Reuben's Restaurant, Franschhoek, South Africa.