Preheat an oven to 170C/150C fan.

Line a big baking tray with baking parchment.

Put the egg whites into a bowl and beat with electric mixer until stiff.

In another bowl mix the ground almonds and caster sugar; add approximately a third of the beaten egg whites and the Amaretto liquor, and stir.

Fold in the rest of the egg whites and stir until the mixture turns into a smooth paste.

Take a portion of the mixture and form a 4-5cm ball, roll it in almond slices and place on the baking tray. Repeat with the rest of the paste (you will end up with approximately 20 cookies).

Place the tray in the oven and bake for 20-23 minutes (they should be still white or light golden).

Take them out from the oven.