Using a citrus zester, remove the zest from all of the lemons. (Alternatively, using a paring knife or a vegetable peeler, remove the zest, then scrape as much of the bitter white pith off as possible.) Roughly chop zest; transfer to the bowl of a food processor fitted with blade attachment.
Add 1 cup sugar to the zest in the food processor. Pulse until zest is finely ground, about 3 minutes.
Transfer the ground mixture to a medium bowl. Add remaining cup sugar, and toss until evenly mixed.
Spread the lemon sugar on a baking pan, and let sit at room temperature until dry, about 1 hour. Store the sugar in an airtight container in a cool, dry place for up to 1 month.
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