INGREDIENTS
1 1/2 lb
chicken breasts
sea salt and black pepper,
5 tbsp
butter, divided
1
medium onion, thinly sliced
1/2 cup
chicken stock
1 cup
heavy cream
2 tbsp
balsamic vinegar
8 oz
cremini mushrooms, halved
1/2 cup
grated Parmesan cheese
2 tbsp
chopped fresh flat-leaf parsley