Add all the wet ingredients to a bowl and mix well. In a separate bowl, mix all the dry ingredients together. Gradually add the wet ingredients to the dry ingredients until well combined and a dough forms.   Knead dough well for 5-10 minutes. Put the dough in an oiled bowl and cover. Fridge the dough for one hour. In a pan, add 1 tablespoon of Colavita Olive Oil and the diced onion. Fry on med-low heat for 45 minutes, stirring every 5 minutes. Remove the onion and add 1 tablespoon of Colavita Olive Oil. Add the Kasha (Buckwheat), salt and pepper. Stir well.  Add 1 cup of water, bring to a boil and cover. Simmer for 10-15 minutes.  In a bowl combine the kasha, onions and mashed potatoes. Stir well. Roll out the dough into a large rectangle. Put the filling across the dough longways 2 inches from the bottom. (See picture for reference). Egg-wash the bottom and top of the dough and roll longways. Roll the log so that it is closed tightly. Use the palm of your hand to create dents in the log every 2 inches. Use a knife to cut where you dented. (See picture 2 for reference) Face the dough upwards so the open part is facing up. Use your thumbs to push the dough into the center. (See picture 3 for reference) Put on a baking sheet and egg-wash generously. Bake for 30-40 minutes until the top appears golden brown.