✓ Wash and slice 12 large mushrooms (white or cremini) into thick rounds; peel and slice 2 large yellow onions thinly.

✓ Heat 2 tablespoons of butter in a large pan over medium heat until it melts completely; add the sliced onions and sauté for 20-30 minutes or until they turn golden brown, stirring occasionally to prevent burning.

✓ Add 3 cloves of minced garlic to the pan and sauté for an additional 2-3 minutes or until the garlic is fragrant but not burnt.

✓ Pour in 1/4 cup beef or vegetable broth and stir well to scrape any caramelized bits from the bottom of the pan, creating a rich base for your soup.

✓ Add the sliced mushrooms along with 2 teaspoons of fresh thyme (or chopped parsley) to the pan; simmer for about 10 minutes or until the mushrooms are tender but still hold their shape, stirring occasionally.

✓ Transfer the mixture into a deep pot and bring it to a simmer over low heat; let cook for another 5-7 minutes to meld all flavors together.

✓ Combine 1/2 cup of Gruyère cheese with 1/4 cup of grated Parmesan in a small bowl, ensuring they are well mixed.

✓ Ladle the soup into oven-safe bowls or soufflé dishes; sprinkle the cheesy mixture over each portion and place under the broiler for about 2-3 minutes until bubbly and golden brown.