Place apricots in a shallow dish and cover (just) with boiling water. Allow to sit and soften, they will become raisin-like.
Meanwhile, combine flour, cinnamon, brown sugar, and salt in a bowl. Add butter in small pieces and mix until mixture looks like coarse sand.
Beat together egg yolk and lemon juice and pour into flour mixture while mixer is running. Mix well, and if dough seems a little dry, add a little extra lemon juice.
Now knead mixture gently by hand and form into a ball. Flatten into a disc shape and chill for 10 minutes before using.
Preheat oven to 425 degrees.
Roll out pastry on a floured surface and place in a 9 inch tart or pie pan, forming it up the sides.
Prick pastry with a fork, line with tinfoil and place a pie weight on top. If you don't have a pie weight, simply line with foil, and place a heavy baking dish right on top of the foil. This will prevent the pastry from puffing up while baking, and keep it tart-like.
Bake 15 minutes, remove foil and weight and bake for 5 minutes longer.
Reduce oven temp to 375 degrees.
Place ground almonds on a cookie sheet and bake for 3 minutes, cool.
Drain water off apricots. If using whole apricots, cut each apricot into 6-8 small pieces.
Combine almonds, butter, sugar and chopped apricots in a bowl.
Add salt, eggs and reserved egg white and mix well.
Pour onto cooled baked tart shell and bake 25 minutes or until set.
Place orange slices on top. Melt jam on stove and brush top of tart with glaze.
Bring whipping cream to a slow boil in a pan, stirring often. Pour over chopped white chocolate and stir until chocolate is smooth and melted.
Cool completely in refrigerator to let mixture become thicker.
Cut and serve tart, stir cold chocolate cream mixture again and drizzle over tart portions on plate.