Cook 8 ounces sliced cremini mushrooms in butter in a large skillet over medium-high heat, 4 to 5 minutes. Season with salt and pepper. Add 1 teaspoon each chopped garlic and thyme; stir 1 minute, then remove to a plate. Add 1 1/4 cups chicken broth, 2 tablespoons butter and a pinch of salt to the skillet. Bring to a boil, then pour over 1 cup couscous in a bowl. Cover and set aside 5 minutes. Stir in some chopped parsley and the mushrooms.