Putt all the ingredients (without jam) in a dish and knead with your hand quickly to get a fragile dough.

Cover the dough with a foil and place it in the fridge for 2 hours.

Make round biscuits. Cut the middle of half of these biscuits out. Bake at 160°C for about 12min.

Uncut halves spread with jam and cover them with cut ones. Sprinkle with caster sugar.