Soak 4 wooden skewers in cold water for 30 mins. Meanwhile, make the glaze by mixing together the bbq sauce, vinegar, honey and mustard in a bowl. Stir through the chopped rosemary and set aside.

Peel the onions, but keep them whole. Top and tail, then cut each onion into 1.5cm thick slices. Line up 3-4 of the slices flat on your chopping board then carefully insert a skewer through the centre of the slices (as you would a lollipop or kebab). Repeat with the remaining skewers and onion slices.

Brush the bars of a preheated barbecue or griddle pan with oil. Coat the onion slices with a little of the glaze and place on the grill. Cook for 20-25 mins until charred and tender, turning the skewers and brushing with more glaze regularly. Garnish with the fresh rosemary sprigs and drizzle over any remaining glaze to serve.