Work the butter, Siúcra/McKinney's Icing Sugar, wheat flour and egg yolks together. Allow the dough to stand in the fridge overnight.
Roll the dough out thin and cut out round cakes of approx. 6 cm in diameter. Make a round hole in half of the cakes. Place the cakes on baking trays lined with baking paper and bake the biscuits with marmalade in the middle of the oven at 200°C for approx. 10 minutes. Spread marmalade on the cakes without holes and place the cakes with holes on top.
Bake the cakes for a further 1-2 minutes.
If you do not make holes in the cakes, you can glaze and decorate them as you wish.