Preheat your oven to 180 degrees.
Spritz the holes of your mini muffin/cupcake tray with low calorie cooking spray.
Cut the pastry into squares of approximately 2.5".
Arrange a square of pastry into one of the baking tray holes, gently pushing down so it forms your tart shape. Brush with a little beaten egg. Add your next square on top, again pushing down to keep the shape. Brush with a little beaten egg again, and then place the third and final sheet on top and brush with the beaten egg. Repeat this process so you have 12 completed tart cases. Remember that you want them to look nice and rustic, so the sheets shouldn't be placed directly on top of each other.
Bake in the oven until starting to turn brown and crispy.
Remove from the oven and carefully add a teaspoon of mincemeat into each case.
Return to the oven and bake for a further 5 minutes to heat through the mincemeat, keeping a close eye on them so they don't burn.
Serve warm, dredged with a little icing sugar, and enjoy!