1. Use a vegetable peeler to remove the peel from the lemons in long strips. Trim away and discard any white pith with a paring knife. In a large jar with a tight-fitting lid, combine the lemon peels with the vodka. Cover and set aside at room temperature for 2 weeks, until the lemon peel is pale and the liquid is a rich yellow color.
2. In a medium saucepan set over medium heat, stir together the sugar and water. Heat until the sugar dissolves, about 5 minutes. Set aside to cool completely. Combine the simple syrup and the lemon-vodka mixture, cover again and set aside at room temperature for 1 day. Strain the lemon peel out of the liquid and discard. Transfer the limoncello to bottles and serve chilled.