In a large skillet over medium heat, melt butter then add mushrooms; sprinkle black pepper and sea salt. Sauté mushrooms until soft. Add garlic and sauté for 2 minutes. Add wine and cook until it reduces by half. Add broth, sherry and cream; stir well. Bring to a simmer. Mix cornstarch with water. Stir in cornstarch mixture until the sauce starts to thicken, about 1 minute.
Add the remaining ingredients except parsley. Reduce heat to medium-low and cook for 10 minutes. Taste and adjust seasoning if needed. Just before serving, stir in parsley. Spoon sauce over grilled chicken breasts or pork and serve with mashed and veggies.