From a 1954 Hungarian Cookbook

POTATO BISCUITS
Makes about 24 biscuits

1 teaspoon salt
1 3/4 cups flour
1 cup cold butter
2 tablespoons sour cream
1 cup cold mashed potatoes
4 egg yolks
2 tablespoons caraway seeds

Sift the salt with the flour. Cut in the butter until well mixed. Add the cream, potatoes, and 3 of the egg yolks. Stir and knead together. Roll thin. Fold over 4 times and chill until firm. Repeat the rolling, folding, and chilling process 3 times. Roll out 1/4 inch thick, brush with remaining egg yholk, and sprinkle with caraway seeds.

Bake in a hot oven (400 degrees F) about 15 minutes, or until light brown.