Using an electric mixer with the paddle attachment, or by hand, mix together the butter and light brown sugar
Add the egg and vanilla, and mix in
Then add the flour, baking powder and mixed spice, and mix in until a dough forms
Divide the dough into 12 pieces, using scales for accuracy if you like. Mine were 50g each
Flatten out each piece of dough into a disc using your hands. Spoon a teaspoon of mincemeat into the centre, then fold the dough around it and pinch the dough together to seal the mincemeat inside. Roll the dough into a ball
Once you have done this with all of the pieces of dough, put them all in the freezer for 30 minutes
Meanwhile, pre-heat your oven to 180C Fan/200C/400F/Gas Mark 6, and put a lined baking tray (or two if you have another) into the oven to pre-heat too
After the 30 minutes is up and your oven is pre-heated, place the frozen dough balls onto the pre-heated baking tray(s), leaving space between them to spread
Bake for 13 minutes, or until the edges are just starting to go golden
Leave to cool on the baking tray(s)
Mix the icing sugar with the water to make a thick, but pourable, paste. Drizzle or pipe it over the cookies
Store leftovers in an airtight container and eat within 3 days