For the chicken salad with prawns, preheat the oven to 220°C (gas mark 7).
Salt the chicken, put it in a roasting tin, drizzle with olive oil and put half a lemon in the cavity of the belly.
Roast the chicken in the oven for 15 minutes, then reduce the temperature to 180°C (gas mark 4), baste the chicken with the gravy and cook in the oven for a further 50 minutes until clear juices run out of the thigh when pierced.
Cool in roasting pan, bone and cut into bite-sized pieces.
Refrigerate until ready to use.
For the dressing, put the egg yolk in a bowl with 2 tsp of warm water, add the mustard, sugar, salt and pepper and whisk everything together.
Gradually add the oil and whisk until you get a thick sauce.
Add the tarragon vinegar while whisking, then stir in the crème fraîche and tarragon.
Season to taste, mix in the chicken and shrimp, and refrigerate for up to 2 hours.
Then transfer the salad to a serving bowl, sprinkle with the flaked almonds and serve on crisp green lettuce leaves.