Step 1Melt 1 or 2 tablespoons of butter in a large, deep skillet over medium heat. Add the mushrooms, sprinkle them lightly with salt and pepper. Cook until tender, about 3 minutes. Remove the mushrooms and keep them warm.
Step 2Melt the remaining 2 tablespoons of butter in the pan over medium-low heat. Add the onion and cook, stirring occasionally, until it is soft but not brown, about 7 minutes. Add the garlic and rice and cook, stirring, until the grains turn milky white and are coated, about 2 minutes.
Step 3Add the broth, bay leaf, thyme and pepper to taste. Add salt to taste; if using water or unsalted broth, add 1 teaspoon at this point. Stir once and cover. Cook over low heat without stirring until the rice is just tender, about 18 minutes; taste a few grains to check. Let the rice stand, covered, for 10 minutes. Discard the bay leaf and thyme sprig. With a fork, fluff the rice lightly and stir in the mushrooms and chopped chives gently. Taste and adjust the seasoning. Serve garnished with thyme sprigs or whole chives, if desired.