1. Place the hearts for two hours in a pot of cold water. Remove and make cuts so that the hearts resemble "pockets". Immediately remove the vessels, as well as the foils. To enlarge the "pockets", remove some meat from the hearts.
2. Boil the mushrooms, be sure to salt them. The broth that remains after extracting the mushrooms should be set aside.
3 Dice peeled onion, boiled mushrooms and meat from the hearts. Put all these ingredients in a heated frying pan, add a little oil and minced garlic. Then mix them and add spices. Let it stew for about twenty minutes.
4. Fill hearts with stuffing. Sew the hole with cooking thread. We put them in a saucepan with mushroom broth. Add sour cream and mix.
5. Braise hearts for 40 minutes.
6. We take out the hearts and we move them to a heatproof form. Pour the broth in which they have been stewed. Bake for about fifty minutes. The temperature in the oven should be about 185 degrees.