Once they've been combined, add the broth, stir, and bring it to a boil. Reduce the heat to medium-low, cover the pot with a lid, and simmer for 15 minutes.
After that time has passed, turn off the heat and remove the lid. Add about 1 more tablespoon of butter (optional), the reserved browned mushrooms, and the parsley. Put the lid back on and let the Rice with Mushrooms rest for 10 minutes.