Finely chop the chicken fillet and mushrooms.
Heat a frying pan with vegetable oil, fry the mushrooms for 2-3 minutes, then add the chicken to the mushrooms and fry for another 3 minutes. Add salt and pepper.
To prepare the sauce, pour flour into a heated frying pan and bring it to a golden color. Add butter. Then pour in milk and simmer for a few minutes. Finally, pour in sour cream. Simmer until the sauce thickens.
Grate the cheese.
Fill the tartlets with chicken and mushrooms, pour 2 tablespoons of sauce into each tartlet.
Sprinkle the tartlets with cheese, place them on a baking sheet and bake for 15 minutes. The dish is ready, enjoy!