Add mushrooms and cook for 5-6 minutes until golden. Stir in salt, pepper, thyme, then pour in cream and simmer for 3-4 minutes until thickened. Mix in Parmesan if using.
Serve rice in bowls, top with mushroom sauce, and garnish with herbs, Parmesan, or chili flakes as desired.
Notes
For a vegetarian option, use vegetable broth and omit Parmesan.