Cut the mushrooms into 1/4-inch (5mm) slices, finely cut garlic, and parsley.

Heat 1 tablespoon of oil in a large frying pan over high heat, when hot add the mushrooms in an even layer. Don't stir for a minute letting the mushrooms brown, then cook, stirring, for a couple of minutes until the mushrooms are soft.

Reduce the heat to low and add the garlic and herbs, cook for 30 seconds.

Take the pan off the heat, add the chopped parsley, and season the mushrooms with salt and pepper.

If your chicken breasts come with tenderloins attached, remove them and use in another dish (or just pan fry them and serve with the stuffed chicken).

Cut a slit horizontally in the chicken breast, creating a pocket (don't cut the breast all the way through, see photos in the post for reference).

Fill the pockets with mushrooms and 2/3 of the grated cheese. If you have some mushrooms left, reserve them - you can add them later to the sauce. Close the pockets with toothpicks (optional).

Heat the remaining 1 tablespoon of oil in a large pan over high heat. When hot add the stuffed chicken and cook on both sides until browned (the chicken doesn't have to be cooked through at this point, only browned). Transfer chicken to a plate.

Add the butter and finely chopped garlic to the pan, cook over medium-low heat for about 30 seconds or until garlic is fragrant.

Add the wine and cook until it's almost evaporated. While the wine is cooking, scrape with a spatula all the brown bits from the bottom of the pan.

Add the broth, cream, and Dijon mustard, whisk until all the ingredients are combined and season the sauce very lightly with salt and pepper.

Add the chicken back to the pan, cover the pan with a lid and cook over low heat until the chicken is cooked through (it took 13 minutes for me, but the cooking time will depend on how big the chicken is and how long have you seared it). About 5 minutes before the end of cooking time, sprinkle the remaining cheese on top of the chicken.

Transfer the cooked chicken to a plate. If the sauce is too thin, cook it a little bit longer until thickened. Season to taste with more salt and pepper (if necessary), add the remaining mushrooms (if you have any).

Let the chicken rest for 5 minutes.

Serve the chicken with sauce, sprinkle with chopped parsley. Enjoy!