1: Prepare the amount that you need. For a normal tart, use two rounded tablespoonsful of jam, and put in a cup.
2: Add a tablespoon of sugar syrup or water, and melt in microwave oven (not too high) or in a bain-marie.
3: Apply a thin layer of hot apricot glaze with a brush, all over the top of the tart (here a pear and almond cream tart). The layer must be thin, because the glaze should not be noticeable in the mouth: the taste comes from your tart, not from the glaze.
4: If the glaze cools while you are working and starts to solidify, heat again and resume. Your beautiful tart is ready...
5: ...to be serve to your guests.
6: To compare with usual tart.
Remarks
If you find in some bad bakery tarts with a thick (enormous!) layer of glaze (some 3 or 4 mm), you are probably in the shop of a rogue who is trying to cheat on the weight of his tart: leave the place quickly.