Preheat the oven to 180 C (350 F) and line 2 trays with baking paper.
Place the flour, butter, margarine, lard and yeast in a large bowl and use your fingertips to crumble everything together until you have a mixture that resembles wet sand.
Add the cream and the egg yolk and bring everything together with your hands until you have a smooth ball of dough.
Roll out the dough on a lightly floured surface, until it is just under 1 cm thick (1/3 inch).
Use a cookie cutter to cut cookies out of the dough.
Dip one side of each cookie first in the egg white, then in the sugar. Place them on the prepared trays.
Bring together the leftover dough and re-roll it to repeat the process.
Bake for 10 - 15 minutes, until lightly golden. Allow to cool on trays. Makes 30 - 40 cookies.
Happy baking, and merry christmas!
Recipe by Butter Baking at https://www.butterbaking.com/2015/12/22/polish-christmas-cookies/