First, trim the ends off the lemons, then peel them with a paring knife or vegetable peeler, removing as little of the white pith as possible. Your goal is to yield 1 3/4 cups of juice, so start with 8 lemons and work your way up from there, depending on how juicy your lemons are. Pour the juice into a wide-mouthed, non-reactive container, then mix in 1 3/4 cups of sugar and stir it into the juice until it is completely dissolved. Next, express the oils in the peels by squeezing them in your hands over the juice mixture with six 4″ sprigs of rinsed rosemary, then drop into the juice mixture. Stir the mixture and macerate it with a spoon to release more of the oils. Cover, then infuse in the refrigerator for 72 hours. Once infused, strain the mixture into a carafe, yielding approximately 2 1/2 cups.