Remove the peels from 10 lemons and place in the bottom of large glass jar. Add 750 mL bottle of vodka and store in a cool place for 1 week, shaking daily. On the 6th or 7th day, mix together a simple syrup using 2 c. sugar and 3 c. water. Add the cooled mixture to the limoncello jar and reseal. Set aside for 3 weeks, shaking daily.