Put the mayonnaise, cream and vinegar into a bowl, with salt and cayenne pepper to taste.
Stir in the chopped tarragon and mix well.
Cover and set aside.
Arrange the lettuce leaves on 4 individual plates.
Peel the pears and scoop out the cores with a teaspoon.
Place one pear on each plate.
Spoon over the tarragon mayonnaise and garnish with lemon twists.