Whisk together the egg yolks and sugar in a large bowl until light in color and a bit fluffy. They don't need to really increase too much in size or anything but you want most of the sugar to dissolve.

Add the vanilla and sour cream and whisk together.

Next, slowly add the buttermilk, making sure to continuously whisk so there are no lumps.

Finally, add the lemon zest and slowly pour in the lemon juice while whisking so the mixture doesn't curdle.

Place this in the fridge for an hour or two so that the koldskål flavors really come together.

Combine the dry ingredients - flours, sugar, salt, baking powder, cardamom, and lemon zest - in a large bowl.

Then, cut the cold butter into small pieces and add to the dry ingredients. Using your fingers, rub the butter into the dry mixture until it breaks up into smaller pieces and the mixture resembles sand.

Next mix together the egg, vanilla, and milk in a separate small bowl. Add this to the dry mixture and combine until it forms a dough. Refrigerate the dough for at least an hour.

Preheat the oven to 350 F (175 C). Shape the dough into balls and put on a lined baking sheet. Bake for 12 minutes or until a light golden color (but still a bit soft!).

Remove them from the oven and lower the oven temperature to 200 F (95 C).

Cut the cookies in half while they are soft and place back on the baking sheet with the cut sides facing up. Bake for 60 more minutes or until the cookies are completely crispy.

To serve, simply ladle some koldskål into a bowl and top with fresh fruit (if you like) and kammerjunker (either whole or crushed up). Enjoy!