Preheat the oven to 180°C.
Line a baking sheet with parchment paper.
Unroll the pastry and stamp out tree shapes, using cookie cutters. Put half of them onto the baking sheet. Drop a small spoonful of mincemeat onto the middle of the trees, then gently spread them out a bit – but not reaching the edges.
Brush the edges with the egg, then cover them with the remaining tree shapes, pressing together their edges.
Using a sharp knife cut a line in the middle of the top layer (for the trunk) and a couple of branches (these will allow the steam to escape and some mincemeat jus to come through). Brush the tops with egg, if you want them shiny looking.
Bake for 10-15 minutes until golden.
Let them cool on a wire-rack, then dust them with icing sugar.