Stir together vegetable mixture and rice. Drain artichoke. Remove center leaves and choke from artichoke. Spread the artichoke leaves slightly. Spoon rice stuffing into the center and behind each large leaf. Return artichoke to casserole. Cover with vented clear plastic wrap. Micro-cook, covered, on 100% power for 1 to 2 minutes or till stuffing is hot and base of artichoke is fork-tender, rotating the casserole a half-turn every 30 seconds. Let stand, covered, while preparing sauce. For sauce, in a 1-cup measure stir together chicken broth, 1/2 t lemon juice, cornstarch, and pepper. Micro-cook, uncovered, on 100% power for 1 to 2 minutes or till thickened and bubbly, stirring every 30 seconds. Stir HALF the hot mixture into the egg yolk. Return all to the 1-cup measure. Micro-cook, uncovered, on 100% power for 15 seconds. Transfer stuffed artichoke to a warm plate. Pour sauce around the artichoke.