- Heat oven to 220°C. Place the potatoes in a roasting tin, then rub with 1 tbsp oil and a sprinkling of salt. Roast for 20 minutes, then add the onion wedges to the tin, giving everything a good shake. Roast for 20 minutes more until the potatoes have turned a deep golden brown and the onions have caramelised and softened. Leave to cool slightly.
- Heat a non-stick frying pan. Dry-fry the bacon until crisp. Add the sliced mushrooms, then fry for 5 minutes more until they have softened.
- Meanwhile, make the dressing. Whisk the mustard, vinegar and remaining 1 tbsp oil with a splash of water. Place potatoes, onions, bacon and mushrooms in a large bowl with the salad leaves, pour over the dressing, then toss well. Divide between 4 plates, then crumble over the blue cheese.