Step 1

Preheat oven to 180°C. Cook bread in oven following packet directions or until golden brown and cooked through. Remove from oven and set aside for 5 minutes to cool slightly.

Step 2

Meanwhile, melt the butter in a large non-stick frying pan over medium heat until foaming. Add the onion and cook, stirring, for 5 minutes or until soft. Stir in the vinegar and sugar and cook, stirring, for 5 minutes or until the onion caramelises. Remove from heat and set aside until required.

Step 3

Meanwhile, heat a large non-stick frying pan over medium-high heat. Add the beef burgers and cook for 3 minutes each side or until brown and just cooked through.

Step 4

Split the bread squares in half. Place bases on serving plates and top with spinach leaves, beef burgers and caramelised onion. Place remaining bread halves on plates and top with cheddar and gherkins. Serve immediately.