In a medium pot, heat Unsalted Butter (2 tablespoon) over medium-high heat until starting to foam.
Add White Mushroom (8 ounce) and stir to coat in butter. Cook until mushrooms are browned and liquid has cooked out, stirring only once or twice, about 5-7 minutes.
Add Vegetable Broth (1 3/4 cup) and bring to a simmer. Stir in Long Grain and Wild Rice (1 cup), Italian Flat-Leaf Parsley (1 tablespoon), Fresh Thyme Leaves (1 teaspoon), Salt (1/4 teaspoon), and Ground Black Pepper (1/8 teaspoon) and allow to return to a simmer.
Cover and reduce heat to low and cook for 23-25 minutes until rice is tender.
Remove from heat and allow to rest for 5 minutes.
Add remaining Unsalted Butter (2 tablespoon) and fluff with a fork. Garnish with additional chopped parsley if desired and serve immediately.