Peel the potatoes and cut them into thin slices with a knife or with a vegetable cutter.
Roll out a layer of puff pastry on baking paper. The size should be approximately 40×20 cm. Put the sliced potatoes on a dough sheet, stepping back 6-7 cm from the edge. Salt and pepper the potatoes well.
Cut the peeled onion into thin rings.
Place the onion on top of the potatoes.
Cut the fish fillet into small cubes.
Put the fish fillet on top of the onion. Salt and pepper the fish.
With a knife, we make cuts along with the dough, as shown in the photo.
From one edge at the top, put the top piece of dough in the middle, as if sealing the cake. And then alternately cross the strips of dough and weave something like a braid. We also turn the bottom edge of the pie inward.
Transfer the cake directly on baking paper to a baking sheet. We send a baking sheet with a pie into an oven preheated to 190 degrees for 40-50 minutes.
We take the finished cake out of the oven and let it cool slightly. Cut the pie into portions and serve. The pie is good both cold and hot.