Mushroom Croissant Filling

Name: Mushroom Croissant Filling
Ingredients: 1 pound mixed mushrooms, such as cremini and shiitake, cleaned and thinly sliced; 2 tablespoons unsalted butter; 1/2 cup yellow onion, finely chopped; 2 cloves garlic, minced; 1 tablespoon all-purpose flour; 1/4 cup heavy cream; 2 ounces cream cheese, softened and full-fat; 1/2 cup Gruyère cheese, shredded; 1 teaspoon fresh thyme, chopped; 2 tablespoons fresh parsley, finely chopped; 1/2 teaspoon kosher salt, plus more to taste; 1/4 teaspoon freshly ground black pepper, plus more to taste