Heat the oven to 180°C/350°F/Gas 4. Line a baking tray with parchment paper.
Put the sugar and butter in a large mixing bowl and beat until light and fluffy.
Add the almond extract and egg yolk and briefly beat to combine.
Sift in the flour into a bowl and add the ground almonds - stir until the mixture is combined.
Use your hands in the end to pull the ingredients together and press the dough into a cylinder shape – approx 8cm in diameter.
Wrap in cling film and chill for 30 minutes in the fridge.
Remove the stick of dough from the fridge and, using a sharp knife, slice off 1cm thick rounds.
Place on the baking tray and spinkle a few flaked almonds on top of each biscuit.
Bake for 10-12 mins until pale golden, then lift onto a wire cooling rack to crisp up.