Prepare a bowl of cold water large enough to hold the 6 artichoke hearts. Add the juice of 2 lemons to the water. Use a paring knife to trim the dark green skin from the stem and the base of each artichoke. Also slice about 2 to 3 inches off the top. In a circular motion, using a paring knife or peeler or your hands, peel the outer, dark green bitter layer of the heart until the fleshly, light green part is exposed. Trim and leave about 2 to 3 inches of the stem. Use a tablespoon to scoop out the "hay" or "choke" from the center of each artichoke. Squeeze some of the remaining lemon juice over the artichoke, if desired, rubbing the lemon directly on them to prevent them from discoloring, then submerge them in the lemon water.
Preheat the oven to 350 degrees F.
In a large bowl, combine 1/4 to 1/2 cup olive oil, the bread crumbs, parsley and fennel with the fontina and Parmesan. Stir to blend. Season with salt, to taste. Remove the artichokes from the water, pat dry and transfer them to a bowl. Reseason with salt and drizzle them with about 1 tablespoon of olive oil. Stuff each artichoke with the bread crumb mixture and arrange them in a flameproof baking dish. Don't be afraid to pack the stuffing into each artichoke. Arrange them close together in the dish so they steam a little and create moisture as they cook. Top the artichokes with any remaining stuffing. Add a little water to the bottom of the baking dish to prevent the artichokes from drying out or scorching on the bottom as they cook. Cover the dish with a tight layer of aluminum foil and put the baking dish in the center of the oven.
After 45 minutes, remove the dish from the oven. Test the most tender part of the artichoke, where the stem and the heart meet, with the tip of a knife. The knife should pierce and remove without resistance. Remove the foil and put the dish under a broiler for 5 minutes. Remove the baking dish from the oven and allow to cool for a few minutes before serving. Cut each artichoke in half to reveal the stuffing, arrange on serving plates and serve.
Since the stem is edible, why cut it off? Plus, the stem makes for a more beautiful presentation.