• Whisk the warm milk, sugar, and yeast in a large bowl. Cover with a kitchen towel and leave for 5 to 10 minutes or until the mixture is foamy. Mix in the egg yolks, oil, flour, and salt. Place the dough on a lightly floured surface and knead until you get a smooth elastic dough, it will take you about 10 minutes. Place the dough in a clean bowl and cover with plastic wrap. Leave for 1 to 3 hours, until the dough doubles in size.
• To make the filling:
• In a small saucepan, combine the buckwheat, 1 2/3 cups water, and a pinch of salt. Bring to a boil over medium-high heat. Change the heat to low and cover the pot with a lid. Continue cooking for 12 minutes, until the buckwheat is soft, but not mushy.
• In a separate saucepan, place the diced potatoes and cover with cold water. Bring to a boil and cook until potatoes are soft. Remove from the heat and mash with 1 tablespoon of butter into a smooth puree. Set aside.
• In a medium pan, heat the remaining butter and oil and fry the onion until golden and crispy, for about 10 minutes. Combine the fried onion, buckwheat, mashed potato, and chives in a large bowl, season to taste with salt.

To assemble the pie:

• Preheat the oven to 375F. Brush the 8-inch springform metal baking pan with melted butter or oil, set aside.
• Punch down dough and place it on a lightly floured surface. Divide it into two pieces, one large and the other is tennis ball-size. You will need a smaller part to make decoration for your pie. If you don’t want to do it, then simply omit that step and don’t divide the dough.
• Roll out a larger portion into a big 1/4-inch thick circle. Mound the filling in the center of the circle and carefully fold the edges together, sealing them on top. You will get a ball-shaped pie. Lightly press it with your hands to make it approximately 8 inches in diameter. Place the pie seam side down into the baking pan and prick the top of the crust a few times with a fork to help release the air sitting baking. Brush the pie with the egg wash. Use the remaining dough to decorate the pie as you wish. Place the decorations on top of the brushed pie, and cover them with a think layer of the remaining egg wash. Sprinkle with sesame seeds and caraway seed.
• Bake the pie for 40 to 50 until golden brown. Remove from the oven and let cool for at least 10 minutes before slicing. This pie tastes fantastic with a side of creamy mushroom sauce or a dollop of sour cream.