Fresh lemonade seems to be just the thing for picnics or barbecues, and making it couldn't be simpler. This perennial favorite requires just 3 ingredients: lemon juice, sugar, and water. This means it won't take much time away from a leisurely summer afternoon to mix a batch. To make 2 quarts, pour 3 cups of fresh lemon juice (from about 20 lemons) through a fine sieve into a pitcher. Add 2 cups of superfine sugar, and stir until it has dissolved. Stir in 4 cups of water and some ice, and then garnish with lemon slices.