Crumble yeast in lukewarm water with 1 teaspoon sugar; let stand until dissolved.

Mix flour, 2 tablespoons sugar and margarine as for pie crust.

Add egg yolks, sour cream, and the dissolved yeast mixture to the flour mixture.

Knead to form a soft dough.

Refrigerate the dough overnight.

Roll out the dough on a lightly floured surface to about 1/2-inch thickness.

Cut out small circles using a doughnut cutter.

Place the circles on a cookie sheet, arranging them so they are touching.

Let the dough rise until doubled in size.

Make an imprint in the center of each circle.

Fill the imprint with prepared pie or poppy seed filling.

Bake at 375°F (190°C) for 25 minutes.