Grilled fresh artichokes make a lovely appetizer course or a great party food. Steaming the artichokes can be done hours or even a day in advance, and they can be tossed on the barbecue just before serving. Here the artichokes are brushed with a simple vinaigrette before grilling, then drizzled with the remainder at serving time.
Squeeze the juice of 1 lemon into a bowl of cold water and set aside. Cut the remaining whole lemon in half and set aside.
Cut off and discard the bottom 1/2 inch of the stem of one artichoke. One by one, bend back the tough outer leaves at the base of the artichoke until they snap, and then pull down sharply to remove the tough skin. Working in a circular fashion around the artichoke, break back the bottom 2 or 3 rows of leaves to expose the paler green leaves beneath (you don't have to continue further). Using a vegetable parer, peel the stem and remove any dark green skin at the base of the artichoke where you removed the outer leaves; this portion of the plant is very fibrous and inedible. Rub the exterior of the artichoke and the stem with one of the cut lemon halves to prevent discoloration. With a very sharp knife, cut off the top quarter of the artichoke and discard. Cut the artichoke lengthwise in half or quarters (depending on how you intend to serve the artichokes) and rub the cut surfaces with the lemon half. Transfer the artichoke wedges to the bowl with the lemon-acidulated water. Repeat with the remaining 5 artichokes.
Steam the artichokes until just tender, 15 to 20 minutes. Remove from the pan with tongs and place the artichokes upside down on a plate to drain and cool. Pull the tight core of purple-tipped leaves from the center of the artichoke and carefully scrape out the hairy choke with a small spoon or melon baller. At this point the artichokes can be refrigerated, covered, for a day before grilling.
Whisk together the olive oil, lemon juice, and garlic, and season with salt and pepper to taste. Brush the surfaces of the artichokes with the mixture and grill over medium-high heat, turning occasionally, until the vegetables are lightly charred in places, 6 to 8 minutes. Transfer the artichokes to a platter and drizzle with the remaining vinaigrette, or serve with dipping sauces of your choice.