2) Cut the onions in half and slice 1/2cm thick, place on a baking sheet and toss with: 60ml balsamic vinegar, 60ml olive oil, 1 tsp salt and 1/2 tsp pepper.
3) Bake for 12 to 15 minutes, until the onions are tender.
4) Remove from oven and toss with 2 more tbsp balsamic vinegar and cool to room temperature.
5) Whisk together the shallots, mustard, red wine vinegar, 1/2 tsp salt and 1/2 tsp pepper in a small bowl. While whisking, add 180ml olive oil until emulsified.
6) To assemble, toss enough lettuce for 6 people with dressing, to taste. Place the lettuce on 6 plates and arrange the onions on top. Sprinkle with salt and pepper and serve.