For the gratinated chicken fillets on tomato sauce, finely chop onion and garlic cloves, cut leek into rings.
Sauté onion and garlic in 2 tablespoons of oil, sprinkle with sugar and caramelize slightly.
Add tomato paste, let it sweat and deglaze with tomatoes and broth. Then season with salt and pepper, simmer for about 8 minutes and season with sherry.
Preheat oven to 180°C convection oven. Fry chicken fillets in 3 tablespoons oil on both sides for about 2 minutes and season with salt and pepper.
Pour tomato sauce into a large baking dish, place cutlets on top and pour creme fraiche on top. Bake in preheated oven for about 14 minutes.
Sauté leeks in 2 tablespoons hot oil. Arrange the gratinated chicken fillets and sprinkle with leek and pepper.