1. Cut the lemon in half. Squeeze the juice from half the lemon into a medium bowl and fill the bowl halfway with cold water. Trim the artichokes. Cut them into wedges about 1/4-inch thick and put them in the bowl of lemon water to prevent them from discoloring.
2. Peel and finely chop the onion. Put it in a heavy-bottomed braising pan with 2 tablespoons of the olive oil. Place over medium-high heat and sauté until it turns a rich golden color, about 5 minutes.
3. While the onion is sautéing, peel and chop the garlic. Finely chop enough of the parsley leaves to measure 1/4 cup. When the onion is ready, add the garlic and parsley. Cook for about 1 minute, then add the drained artichokes. Stir until the artichokes are well coated, then season with salt and pepper. Add about 1/2 cup water, cover the pan, and turn the heat down to medium. Cook until the artichokes are tender, 10-15 minutes, by which time all the water should have evaporated. If all the liquid evaporates before the artichokes are tender, add a little more water.
4. While the artichokes are cooking, put the broth in a pot over high heat and bring to a boil. Lower the heat to maintain a very gentle simmer.
5. Raise the heat under the artichokes to medium-high. Add the rice and stir until it is well coated. Add about 1 cup of the hot broth and continue stirring. Add only enough broth to produce the consistency of a rather thick soup and wait until all the liquid is absorbed before adding more. Season with salt and continue until the rice is al dente, 20 to 25 minutes.
6. Remove the risotto from the heat, stir in the remaining 1 tablespoon olive oil, and serve at once.