Melt butter and sauté mushrooms, celery, shallot and garlic until softened.
Add thyme, then chicken broth.
Bring to a boil. Add rice, stir and remove from heat.
Let stand for 10 minutes.
If using regular rice (not instant), add it to the pan before the broth and stir it into the vegetables before adding the broth.
You may have to adjust the amount of broth you need, based on the ratio of water you need for the type of rice you choose to use.