In a large bowl mix the flour and the cubed butter to a crumbly mixture. Work with your fingertips so that you don't melt the butter.
Add the icing sugar and the lemon peel and combine well.
Form a well with the ingredients, put the egg in the middle and start mixing. Knead the dough briefly until all the ingredients are incorporated and a smooth dough is formed.
Wrap in cling film and let it rest in the fridge for at least 30 minutes.
Meanwhile preheat the oven to 180°C or 350°F. Line a baking tray with parchment paper. Set aside.
Roll out the dough on a floured surface until it's about 0.5 cm thick. Cut the dough with a smaller cutter and cut out the centre of half of the biscuits.
Transfer to the baking tray, leaving some space between one another, and bake for about 20 minutes, until they turn slightly golden brown at the edges.
Leave to cool at room temperature on a cooling rack.
Once all the biscuits have cooled a little but are still a bit warm, dust the biscuits having the cut out centre, with icing sugar.
Add about a teaspoon of lemon curd to each of the full biscuit and place the cut out centre biscuit on top of the jam. Thus, sandwiching the curd between the two biscuits.