Preheat oven to 400 degrees F. Trim tips of artichoke leaves by cutting straight across the tip with a sharp knife, rotating to cut all tips. Cut off all but 1" of stems. Quarter artichokes and cut out the feathery material at the centers. Rub all cut surfaces with the lemon half. Bring a large pot of salted water to a boil and add lemon juice. Add artichoke quarters and boil for about 10 minutes or until tender but still firm. Drain and cut each quarter in half. Place in a baking dish and sprinkle with oil, garlic, salt and pepper and toss to coat. Bake for 30 minutes. Serve with Mustard Mayonnaise. For Mustard Mayonnaise: Blend mayonnaise and mustard together until completed combined in a small bowl.