In a small bowl combine dry yeast, 1 tsp of fine sugar and warm milk. Cover with plastic food wrap and let rise for 10 minutes. This yeast started must double in size.
In a large mixing bowl of standing mixer, combine room temperature butter, sugar and egg yolks. Mix with flat beater attachment, until creamy & fluffy (about 2 minutes). Add yeast starter and mix it in.
In another bowl combine all-purpose flour, salt and zest from one lemon. Change the flat beater attachment for dough hook attachment and alternatively add mixture of flour and warm milk into the batter. Add it slowly; spoon by spoon, do not rush and make sure every time the flour & milk gets well incorporated.
At the end the batter will become lightly sticky inside, but do not stick on the surface to the bowl. If the dough is too sticky, add slowly more flour and if it’s too hard, add little of warm milk or melted butter. The dough has to be soft and pliable. Remove the dough hook attachment and sprinkle the dough with 1 extra spoon of flour. Cover with clean cloth or plastic food wrap and let rise the dough in warm place (no draft) for 2 hours.
When the dough had doubled in its size, sprinkle a bit of a flour on clean working surface and place the dough on it. Cut it in 3 equal pieces.
Take a large piece of parchment paper, big enough to cover regular baking cookie sheet, and place 1 piece of dough on it. Sprinkle the dough with flour and roll thin round shape pie (pizza looking like) in diameter of 35 cm (14″ inches).
Fill the round cake with dry pressed cottage cheese filling, we reserved earlier and leave about 2 cm (3/4 inch) space on the edges. Roll the edges lightly inside, toward the filling, to secure the filling. Repeat the same process with the other 2 pieces of dough and fill them with plum jam and poppy seed mixture. (if you do not have any above fillings, you can use other sort of jams or make more of cottage cheese filling)
Generously sprinkle the frgal cake with streusel, you made earlier. And place the frgal with parchment paper onto the baking sheet. Let it prove again for another 20 minutes.
Meanwhile, the frgal is on its second proving time, place the oven rack in middle position and preheat the oven to 180 C / 356 F.
Before you place the frgal into the oven, brush the edges with whisked whole egg & milk. Bake for 12-15 minutes, until the edges turns golden brown.
Remove carefully from the oven and leave it on the baking sheet for another 10 minutes to cool it down. Continue baking the other 2 pies.
Cut the frgal in triangles, like you are cutting pizza and enjoy it!