Wash and quarter apples, core out the seeds, halve the quarters but do not peel (the peel will give flavor and body). Place apples in a heavy pan along with the juice of the lemon and the zest (yellow part of peel), the cinnamon and l/2 cup of sugar. Cover pan and set over moderately low heat; apples will slowly soften and render their juices. Stir and mash frequently until render throughout-about 30 minutes. Puree through a vegetable mill or sieve back into the pan; simmer, stirring, for a few minutes, adding more sugar to taste. The applesauce should be thick enough to hold its shape in a spoon. Stir in the vanilla.