Combine the water and lemon juice. Working with 1 artichoke at a time, cut off stem to within 1 inch of base; peel stem. Remove bottom leaves and tough outer leaves, leaving the tender heart and bottom. Cut artichoke lengthwise into quarters. Remove the fuzzy thistle from bottom with a knife. Place artichoke in lemon water. Repeat procedure with remaining artichokes. Drain.
Heat oil in a large nonstick skillet over medium-high heat. Add leek, and sauté 4 minutes. Add artichokes, and sauté 2 minutes. Stir in wine; cook until liquid evaporates. Add broth, parsley, tarragon, pepper, and salt; reduce heat, and simmer 2 minutes. Sprinkle with flour; stir in peas, and cook 2 minutes. Remove from heat. Combine sour cream and mustard; stir into vegetable mixture. Spoon vegetable mixture over toast.