Chicken Gloria with Creamy Mushroom Sauce and Parmesan

Ingredients

• 4 boneless, skinless chicken breasts
• 2 tablespoons olive oil
• Salt, to taste
• Black pepper, to taste
• 2 tablespoons unsalted butter
• 1 small onion, finely chopped
• 2 cups mushrooms, sliced (cremini or white button)
• 2 cloves garlic, minced
• 1/2 cup white wine, or chicken broth
• 1 cup heavy cream
• 1/2 cup chicken broth
• 1 tablespoon Dijon mustard
• 1/4 cup Parmesan cheese, grated
• 1 tablespoon fresh parsley, chopped (optional)