By Jill Dupleix
This is even nicer than the more traditional steak sandwich, as lamb teams with sweetly caramelised onions for a hearty weekend lunch.
Heat the oven to 180°C/Gas 4. Finely slice the onions and toss in a roasting pan with 2 tbsp olive oil, the balsamic vinegar, salt and pepper. Bake for 30 to 40