1. Rinse 3 lemons; if waxed, rub with a cloth under hot running water. Dry with a cloth. Grate yellow part (white is bitter) from lemons to make 1 tablespoon.
2. In a 2- to 3-quart pan, combine peel, sugar, and vodka. Stir often over medium heat until mixture reaches 125° to 130° (hot to touch), about 5 minutes. Watch carefully; if overheated, fumes may ignite. Let cool.
3. Meanwhile, cut the 3 grated lemons in 1/2 and ream 8 to 10 tablespoons juice. Add juice to vodka mixture. Pour into bottles; seal airtight. (If seals are rubber or synthetic rubber, cover glass top with plastic wrap to protect seals; alcohol can soften them.) Store at least 2 days or up to 1 week in a cool, dark place. Pour through a strainer lined with 2 layers of damp cheesecloth into an 8-cup glass measure; return to bottles. If desired, pare fourth lemon to get long, thin strips of peel and drop into bottles.