You can make the dough for an open cake yourself (simple, shortbread – one part butter, two parts flour, and two tablespoons of cold water), or you can save time by buying a dough in the store. The filling for the pie is made from mackerel fillets, onions, and beaten eggs with sour cream and herbs. Serve a delicious hot pie with fresh tomatoes and cucumbers.
Preheat oven to 200 degrees. Place the dough in a mold, covering the bottom and sides of the mold (cut off any excess dough). Cover with parchment and evenly sprinkle the bottom with dry peas (or use a special baking weight) to prevent the dough from rising and retaining its shape. Bake for 15-20 minutes, until the edges are golden brown. Remove peas and paper. Brush the base of the pie with yolk and place in the oven for another 2-3 minutes. Remove from oven and reduce temperature to 180 degrees.
Finely chop green onions, chives, and parsley. Disassemble the skinless mackerel fillets into small pieces. Heat olive oil in a skillet over low heat. Add half the green onions, a pinch of salt, and cook for about 5 minutes. Place the fried onions over the base of the pie, along with the raw chives. Arrange the fish slices on top and sprinkle with black pepper.
Whisk 2 eggs with sour cream (or crème fraîche). Add parsley, chives, salt, and stir. Gently pour this mixture over the filling of the pie. Place in the oven for 20-30 minutes. Let sit for 10 minutes and then gently remove the cake from the mold.