1. Preheat oven to 425°.
2. Combine 6 cups water and lemon juice in a large bowl. Cut off stem of each artichoke to within 1 inch of base; peel stem. Remove bottom leaves and tough outer leaves, leaving tender heart and bottom. Cut each artichoke in half lengthwise. Remove fuzzy thistle from bottom with a spoon. Place artichokes in lemon water.
3. Combine oil and potatoes; toss well. Arrange potatoes in a single layer on a jelly-roll pan coated with cooking spray. Bake at 425° for 15 minutes. Drain artichokes; add artichokes to potatoes, tossing to combine. Bake an additional 15 minutes or until tender. Place vegetables in a large bowl. Toss with butter and remaining ingredients. Serve immediately.