Peel the potatoes and cut into thin slices (up to 2 mm thick). Mix egg yolk with mustard.
Salt, pepper, and roll the fish fillet in flour.
Brush the fillet on one side with a mixture of yolk and mustard.
Place the potato slices on the fish fillet in a shingle pattern and press firmly with a paper towel or napkin. Season the potatoes with a little salt and sprinkle with dry basil.
Preheat a skillet with vegetable oil. Using a spatula, gently but quickly enough put (turn) the fillet with potatoes down into the heated oil. Fry fish in potato scales over medium heat for a few minutes until the potatoes are golden brown. Then carefully turn over and fry the fish for another 2-3 minutes.
Then put the fish and potatoes on a baking sheet with potatoes facing up and cook in an oven preheated to 180 degrees for about 10-15 minutes.
You can prepare a salad of fresh tomatoes with fish and potatoes.