How to Make It
Trim and very thinly slice the radishes, carrot, celery, leek and fennel bulb using a manual mandoline-type slicer.
In a large bowl, combine the 3 tablespoons lemon juice with the mustard and beat lightly with a fork; beat in the 3 tablespoons olive oil. Stir in the drained capers and season with sea salt.
Trim the artichoke, rubbing the cut portions with the lemon half as you go to prevent discoloration. Cut off the stem and pull off all the dark outer leaves around the base. Cut the artichoke crosswise about 1 1/2 inches from the base to remove the remaining leaves. Scoop out the hairy choke and trim around the top and bottom of the heart.
Slice the artichoke heart very thin and toss with the dressing. Add the sliced vegetables and toss gently.
Arrange the carpaccio on plates or on a platter. Using a vegetable peeler, shave Parmesan on top. Season with pepper, drizzle with olive oil if desired and serve.