Some cooks prefer to cook large artichokes before trimming, but the following technique makes precooking unnecessary. The trick is to use a knife to cut away the leaves instead of plucking them off by hand.
1. Use a serrated blade to cut away the top of the leaves about halfway between the tip and the base.
2. Hold the artichoke with the stem pointed toward you and make a shallow vertical cut into the artichoke. Then, holding the blade of the knife at an angle, rotate the artichoke, moving the knife in between the tough, outer green leaves and the tender, inner yellow leaves so that the tough green ones fall away.
3. Remove any stray outer leaves by snapping them off at the base. With a small paring knife, trim away any remaining green patches from the exposed inner leaves.
4. Cut away the remaining leaves a half inch above where they meet the base of the artichoke.
5. Remove the green outer layer of the stem and base using a vegetable peeler. Cut off the bottom half inch of the stem and trim away any remaining green parts from the underside of the base.
6. Insert a spoon into the fuzzy choke at the center of the artichoke and scrape firmly along base and rim to scoop out all the fibers.
7. Run a paring knife vertically along the outer edge of the base to remove any remaining leaf stubs.
8. To prevent oxidation, rub the surface of the artichoke base with the cut side of a lemon. Or, place trimmed hearts in water mixed with lemon juice until ready to use.