For the filling:
1) Fill a large stockpot halfway with water and bring to a boil.
2) While water is boiling, take a paring knife and cut a 1cm X on the bottom of each plum. Set aside.
3) Fill a large bowl with ice and water and set aside. When water is boiling, gently drop plums into water for 30 to 45 seconds. Remove with a slotted spoon and immediately submerge in ice water for two to three minutes. Remove and dry plums gently with a paper towel.
4) Over a medium-sized bowl, remove skins from plums - they should slip off fairly easily. Slice plums in half and remove pits. Toss with sugar, cinnamon, and lemon juice and set aside.
For the crust:
1) Preheat oven to 190°C/ gas mark 5.
2) Grind the almonds in a food processor until they are a fine crumb. Add the pastry flour, salt, cinnamon, nutmeg and sugar to the almond in the processor and pulse 5 times to incorporate. Add butter and oil and pulse for about 20 seconds, until mixture forms small clumps. Add the egg white and pulse an additional 20 to 30 times, until mixture forms a ball, being sure not to over-process. Dough will hold together, but be slightly sticky.
3) Evenly press dough into the bottom and sides of a 23cm tart pan with a detachable bottom. Bake for 8 to 10 minutes, or until surface of tart is no longer shiny. Remove from oven and let cool.
4) Place tart shell on a baking tray. Toss plum halves in their own juices in bowl. Arrange plums, cut-side down, in the tart shell, crowding as many plums as you can into tart.
5) Bake for 15 to 20 minutes, or until fruit is slightly tender but still firm. Remove from the oven and let cool.
For the glaze:
1) Heat preserves over a low flame or in microwave until melted. Combine with water and brush surface of tart.