Start by halving the chicken breasts lengthwise to create thinner fillets. Season them generously with salt and pepper. Heat olive oil in a large skillet over medium heat, then sear the chicken until golden brown on both sides. Once done, set them aside on a plate.

Using the same skillet, add the sliced mushrooms. Sprinkle them with rosemary, salt, and pepper, and cook until they’re golden and aromatic. Toss in the chopped shallot and minced garlic, and sauté for a couple of minutes until softened.

Sprinkle the flour over the mushroom mixture and stir well. Pour in the white wine, scraping the skillet bottom with a wooden spoon to release all those flavorful browned bits. This step adds richness and depth to your sauce.

Add chicken stock, heavy cream, and Dijon mustard while stirring to make it smooth. Simmer the mixture for a few minutes. Return the chicken breasts to the skillet, then cook everything together until the chicken is fully cooked and the sauce is thickened.

Plate the chicken and pour the creamy mushroom sauce generously over it. Sprinkle some fresh parsley or rosemary on top, and it’s ready to serve!