Break off the stems of the artichokes, remove most of the leaves, cut off the tips on the remaining leaves and carve off everything that is green on the artichoke bottoms. Immediately pat with lemon juice.
Whisk 1 quart of cold water with the flour, juice of 1/2 lemon and 2 tsp salt and bring to a boil.
Cook the artichokes, uncovered, until soft (20-30 minutes).
Put them in a bowl of cold water.
When cold, remove the rest of the leaves and all "hair" on the bottoms. Put aside.
Boil the beans in salted water until crisp and put in cold water.
Cut off the lower part of the asparagus, saving only the top three inches. Cook the asparagus in salted water until crisp and put in cold water.
Drain the vegetables and pat dry with a kitchen towel. Cut the artichoke bottoms into 1/2-inch pieces.
Make the dressing by whisking the herbs, any liquid from the truffle and salt and pepper with the vinegar and lemon juice. Add the oil.
Mix artichokes, asparagus and beans with the dressing.
Rinse the lettuce and pat dry.
Arrange the lettuce on two plates, put the vegetables in the middle, garnish with the foie gras slices and finely slice the truffle all over the plates. Garnish with a little coarsely ground pepper.