In a mixing bowl, combine the flour, salt, and vinegar. Create a well in the center and add the small egg, oil, and water. Mix until a soft dough forms.
Knead the dough on a floured surface for about 5 minutes until it is smooth. Cover with a damp cloth and let it rest for 30 minutes.
In a separate bowl, combine the soft fresh cheese, 3 eggs, sour cream, salt, and pepper. Mix until the filling is smooth and well combined. Set aside.
Dividing the dough into two parts, roll out one part on a floured surface to fit your baking dish. The dough should be thin but not transparent. Transfer it to the dish, allowing the edges to hang over.
Spread the cheese filling evenly over the rolled-out dough, making sure to cover the entire surface.
Roll out the second part of the dough and place it over the cheese filling. Pinch the edges to seal the pie.
Brush the top with the large egg mixed with a bit of water to create a golden crust.
Preheat your oven to 180°C (350°F). Bake the Placinta Dobrogeana for about 45-50 minutes or until the crust is golden brown. Allow it to cool slightly before slicing.
Optional: Peel and slice the apples. In a pan, melt 50 grams of butter, add the apples, sugar, and a bar of cinnamon. Cook until the apples are tender. Layer this between the dough and cheese filling for a sweet twist.