Clean the cauliflower and broccoli, cut into florets and wash. Cook the cauliflower florets in plenty of boiling salted water for 8-10 minutes. Add broccoli halfway through the cooking time. In the meantime peel onions and cut them into fine rings.
Dice Roquefort. Mix vinegar, salt and pepper. Whip the oil into it. Drain the cauliflower and broccoli and mix with the vinaigrette, onion rings and Roquefort. Leave to stand for about 30 minutes.
Remove the fat from the edge of the salmon ham and place it on 4 plates. Arrange salad on top and serve sprinkled with chervil as desired.