Mix plain flour and baking powder.
Add salt if you are using any.
Add the cold butter and rub it into the flour. Rub it in with your finger tips till the flour resembles bread crumbs.
Add the zest and sugar. Mix well.
Add the egg. Form a dough.
Make the dough into a round ball. Wrap it with a cling film.
Put it in the fridge for 30 minutes.
Preheat the oven to 160°C.
Line a baking tray with parchment paper.
Dust the worktop lightly with flour. Roll the dough to about ¼" thickness.
Cut shapes using a cookie cutter or cutters.
Use a small bottle top or small cookie cutter for the middle. Cut the middle to create a hole.
Carefully place the cut cookies on the baking tray.
Re roll the remaining dough and cut cookies.
Brush the cookies with milk. Sprinkle the toppings of your choice on it.
Bake them for 15-20 minutes till they are lightly pinkish around the edges.
Remove the cookies from the oven.
Allow them to cool in the tray for 2-3 minutes.
Place them on a wire rack to cool completely.
Store them in an airtight container.
Tie them with ribbons and hang them on the Christmas Tree.