Dissolve the fresh or dry yeast in a bowl with lukewarm milk with 1 teaspoon of sugar. Set aside for about 15 minutes until the mixture becomes foamy and doubles in size. 

Place the flour into a large bowl, add the yeast, milk and sugar mixture as well as the egg yolk, sour cream, butter and salt. Mix well with your hands until the mixture starts forming a dough. Knead the dough for about 12 to 15 minutes until it is soft, not sticky and smooth. Cover with a kitchen towel and set aside to res for about 45 to 60 minutes until the dough doubles in size. 

Transfer the dough onto a floured surface and roll it out with a rolling pin into a ¼ inch thick rectangle. The rectangle should be in a vertical orientation in front of you. Sprinkle ⅓ of the grated cheese along the whole surface of the dough. Sprinkle ⅓ of the caraway seeds evenly over the dough and cheese. Press the cheese and seeds with your hands into the dough.

First fold of the dough: Take the bottom edge of the dough and fold it over and onto the dough to meet the center of the dough. Take the top edge of the dough and fold it down and over to meet the bottom edge of the folded layer of dough.Take the right edge of the dough and fold it over to the left and onto the center of the folded dough. Take the left edge of the dough and fold it over and onto the right edge of the folded layers of dough. Gently press down on the folded dough and place a towel over the dough. Let it rest for about 15 minutes.

Uncover the fodled dough and roll it again into a ¼  inch thick rectangle. Sprinkle another third of the cheese and caraway seeds evenly over the dough. 

Fold the dough for the second time: It’s important to fold the dough in the same order that you folded it the first time. Take the bottom edge of the dough and fold it over and onto the dough to meet the center of the dough. Take the top edge of the dough and fold it down and over to meet the bottom edge of the folded layer of dough.Take the right edge of the dough and fold it over to the left and onto the center of the folded dough. Take the left edge of the dough and fold it over and onto the right edge of the folded layers of dough. Gently press down on the folded dough and place a towel over the dough. Let it rest for about 15 minutes.

Uncover the fodled dough and roll it again into a ⅓ inch rectangle. Sprinkle the remaining cheese and caraway seeds evenly over the dough. 

Fold the dough for the third and final time: Take the bottom edge of the dough and fold it over and onto the dough to meet the center of the dough. Take the top edge of the dough and fold it down and over to meet the bottom edge of the folded layer of dough.Take the right edge of the dough and fold it over to the left and onto the center of the folded dough. Take the left edge of the dough and fold it over and onto the right edge of the folded layers of dough. Gently press down on the folded dough and place a towel over the dough. Let it rest for about 15 minutes.

Preheat the oven to 355° F.

Roll out the dough to a rectangle that is about ¾ inch thick. Use a 2 to 3 inch cookie cutter or the edge of a cup to cut out circles of the dough. Place the cut pieces of the dough onto a parchment lined baking sheet. Gather the dough scraps, and reroll the dough to ¾ inches thick. Cut out the remaining pieces of dough and transfer to the baking sheet. Brush the top surface of all the pieces of dough with a beaten egg. Transfer to the oven and bake for about 20 minutes or until the pastries are golden brown. 

Set the baked pastries aside for about 5 minutes and serve warm.