Step 1

Place onion in a deep frypan with lager, sugar, balsamic, oil and 1/2 cup (125ml) water. Bring to a simmer over medium-high heat. Reduce heat to low and cook for 40 minutes or until thick and rich, stirring occasionally to prevent onion catching on the base of the pan. Caramelised onions will keep in an airtight container in the fridge for up to 1 month.

Step 2

Meanwhile, preheat a barbecue or chargrill pan to medium-high. In batches if necessary, cook the sausages, turning, for 6-8 minutes or until cooked through.

Step 3

Warm the bread rolls on a rack on the barbecue or in a low oven, then split through the middle, without slicing all the way through. Fill the rolls with mustard, sausages, caramelised onion and rocket.