Wash and peel the lemons, being careful to avoid as much of the white pith as possible. Place the peels into a large, airtight, sealable jar.
Add the vodka to the jar, close the jar and gently shake. Place the jar in a cool dark place for at least 7 days up to 21 days to let the peels infuse. Gently shake the jar occasionally during that time.
After the 7 to 21 days that you have let the peels infuse, make the simple syrup by combining the sugar and water into a pot. Bring the sugar water to a boil, stirring frequently.
Let the mixture boil for 1 to 2 minutes then remove from heat and cool completely.
While the syrup is cooling, strain the lemon peels out of the vodka and discard the peels. Pour the vodka into the jar.
When the syrup has cooled, combine the syrup with the vodka, and stir well. Pour the limoncello into airtight, sealable bottles.
Store the limoncello in the refrigerator or your refrigerator's freezer (not a deep freezer). Serve chilled.
Notes
Plan your limoncello ahead: Remember you need 1 to 3 weeks to make limoncello from scratch. Adjust the flavors to taste: Use less or more sugar, any brand of vodka and any lemons you like to finetune the flavor. Use a clean jar: Make your limoncello in a clean, better yet sterilized, jar.