PEEL, QUARTER and core the apples. Slice 3 apples into thin slices, toss with lemon juice and 2 tablespoons of the sugar and set aside. Make applesauce with the rest of the apples: Chop coarsely, place in a saucepan with 2-3 tablespoons of water, cover and cook over a medium-low heat until very soft. Warm the jam, then force it through a sieve (fruit bits can be returned to the jar). Add 1/4 cup of strained jam to applesauce, together with the Calvados and butter. Continue cooking, if needed, until fairly thick. Taste and add sugar if needed. It should taste sweet, but not like jam. Spread the applesauce over the tart shell, then layer the drained apple slices in concentric circles over it. Bake about 30 minutes, until the apples are tender. Warm remaining apricot jam, adding a tablespoon or so of water if needed, to paint over the tart. Best served warm.