Step 7: Add 1 tablespoon of butter, diced onions, minced garlic, and thyme sprigs to the pan. Melt butter, season with salt and pepper, and stir to combine. Sauté onion and mushroom mixture for 5-6 minutes, or until the onions are softened. Sprinkle all-purpose flour over the mushroom mixture and stir to combine. Cook for 1-2 minutes, stirring frequently.