Beat the butter and caster sugar together until pale and fluffy. Add the vanilla and egg yolks and mix thoroughly. Gradually add the flour and ground almonds. Lightly knead the mixture until it comes together in a ball. Wrap and chill for 1 hour.
Heat the oven to 170C/fan 150C/gas 5. Roll the dough out to the thickness of a £1 coin on a lightly floured surface and stamp out biscuits using a 6-7cm cutter. Reshape leftover dough into a ball, re-roll and cut out more biscuits. Stamp out a smaller circle from the middles of half the biscuits.
Put the biscuits on lined baking sheets and bake for 12-15 minutes or until golden. You may need to do these in batches. Rest for a minute then transfer to a cooling rack. When completely cold, spread the whole biscuits with either jam. Dust the ring-shaped biscuits with icing sugar. Put a sugar-dusted ring on top of a jam-covered biscuit and press lightly together.