Add the softened butter and beat until light and fluffy using an electric handheld mixer.

Add an egg and heat again until well incorporated, making sure to scrape the sides of the bowl once or twice.

Mix in lemon extract, if using.

Add the flour, and fold it in gently, until rough dough forms. Knead the dough gently, just enought obring it into a ball.

Flatten the dough and wrap it in cling film (plastic wrap) and place it in the fridge for an hour.

Preheat the oven to 180 C Fan. Line a large baking sheet with parchment paper.

Once chilled, form 20-22 small balls and arrange them onto a prepared baking sheet.

Make a dent into each cookie ball with your thumb and add a small amount of lemon curd into each dent (don't fill it to the brim or it will leak out over the edges).

Bake in the preheated oven for 10-11 minutes. Let the lemon thumprint cookies cool down completely on the baking tray.

Serve dusted with a little icing sugar.