To give the apple frangipane tart a shiny finish, you can brush it with a simply syrup when just out of the oven. It is made by reducing the same quantity of water and sugar (and optionally a little bit of vanilla paste) on the stove until it starts to thicken. Alternatively, you could also mix some apricot jam with a little bit of water to thin it out. It will give you a similar sweet glaze effect.