Peel lemons with a sharp vegetable peeler, taking only the zest (top layer) and avoiding any white pith. Put rosemary in a 1-gal. glass or ceramic container with a tight seal. Add zest to jar.
Pour 750 ml. vodka over rosemary and zest; seal container. Let sit undisturbed in a cool, dark place for 40 days.
In a saucepan, bring 5 cups water to a boil and add sugar. Cook, stirring, until sugar has dissolved. Let sugar syrup cool to room temperature, about 1 hour.
Pour syrup and remaining 750 ml. vodka over lemon-vodka mixture, stir, and seal container. Let sit in a cool, dark place for another 40 days.
Pour limoncello through cheesecloth into a large spouted pitcher and divide among gift bottles.
Note: Nutritional analysis is per ounce.