In a bowl, whisk flour, sugar & zest. Add butter & blend with pastry blender until mixture resembles coarse meal. Gradually add the orange juice, using enough to form a dough that cleans the sides of the bowl.
Roll out dough on a lightly floured work surface. Using a 2 1/2-inch cutter, make 12 circles & fit into tart pan cups. Line the pastry with foil & add pastry weights. Bake about 10-15 minutes. Remove weights & foil & bake 10 minutes longer until pastry is golden.
Mandarin Orange Pastry Cream
In a bowl, whisk together egg yolks, sugar & cornstarch until it turns pale yellow.
In a saucepan, combine milk & orange zest; bring to a boil. Remove from heat, slowly add a egg mixture a little at a time, whisking well until fully incorporated.
Return mixture to heat & keep whisking over medium heat until it thickens. Stir in orange juice. Transfer to a bowl & cover with plastic wrap, making sure the wrap touches the surface of the pastry cream. When it comes to room temperature, refrigerate.
When cooled & you are ready to use the pastry cream, whisk with an electric mixer for 15-20 seconds to a smooth & spreadable texture. Spoon filling into baked tart shells. Top each with a couple of mandarin orange slices. Brush oranges with a bit of apricot jelly.
Recipe Notes
If pastry weights are not available, reverse you tart pan & place pastry rounds over the bottoms of tart cups to bake.
If you use canned mandarins for decoration, drain & blot on paper towel to remove excess liquid.