Heat oven to 150C/130C fan/gas 2 and line a large baking tray (or 2 smaller) with baking parchment. Place the egg whites in a large bowl and use an electric mixer to whisk until foamy. Add the lemon juice and whisk again until they hold soft peaks.
Slowly mix in the icing sugar and continue whisking until the mixture is stiff. Remove about a quarter of the meringue mixture and set aside to use for the topping. Put the almonds, cinnamon, ginger and lemon zest in the bowl with the meringue and mix to form a stiff, slightly sticky dough.
To form the stars, put the dough on a piece of baking parchment lightly dusted with icing sugar and dust the top of the dough with sugar, too. Place a second sheet of parchment on top of the dough and roll out to about 0.5cm thick (the dough is a little sticky, so the parchment makes it easier to roll). Peel off the top sheet of parchment and use a 5cm star-shaped cutter to cut out as many cookies as possible. Place them on your prepared baking tray.
Using the reserved meringue mixture, spread a small amount onto the top of each cookie, covering the entire top – you may need to add a few drops of water to make the meringue a little easier to spread. Put the tray in the oven and bake for 12-15 mins until meringue is set but not browned. Allow to cool fully before storing in a sealed container for up to 2 weeks.