Peel or zest the lemons, taking care to just zest the outermost yellow peel and none of the white pith inside. If necessary, carefully cut off any residual pith with a small pairing knife.Place lemons in a large glass mason jar or other glass container than can be sealed airtight. Cover with everclear or vodka. Secure lid and place in a cool, dark location for at least 1 week and up to 4 weeks.When liquor is yellow in color and peel begins to turn white and easily snaps in two pieces when bent, limoncello is done. The longer it steeps the stronger the lemon flavor will be.Strain limoncello into a clean class jar, discarding lemon peels. If desired, strain the lemon liquor again through a fine mesh sieve lined with a coffee filter. This will remove even more residual solids and result in a smoother final product.Combine sugar and 3 cups filtered or bottled water in a saucepan set over medium high heat. Bring to a simmer, stirring occasionally until sugar is completely dissolved. Remove from heat and let cool, then pour into jar with lemon liquor. Secure lid and return to your cool, dark location to mellow, at least 2 weeks or more. The longer you let it mellow, the better your final limoncello will be.Once limoncello has mellowed, use a funnel to divide limoncello among three half-liter glass bottles or equivalent. Chill in the freezer for at least 24 hours before serving.