In a large pot, melt 1 tablespoon of unsalted butter over medium heat. Once melted, add the sliced mushrooms to the pot, spreading them out to ensure even cooking. Sauté for 6-8 minutes, allowing them to brown and caramelize. Remove from pot and set aside.

Using the same pot, add the remaining 2 tablespoons of butter over medium heat. Once melted, toss in the diced onions, chopped celery, shredded carrots, and minced garlic. Sauté for 4-5 minutes until softened.

Sprinkle the all-purpose flour over the sautéed vegetables, stirring vigorously to combine. Cook for an additional minute to activate the flour.

Gradually pour in the half-and-half and chicken broth, mixing well to avoid lumps. Add the dried thyme and black pepper, then bring to a gentle boil. Simmer for 2-3 minutes.

Gently stir in the potato gnocchi and chopped spinach. Continue cooking for approximately 4-5 minutes, or until gnocchi are tender.

Return the sautéed mushrooms to the pot, mixing them in thoroughly. Simmer for another 4-5 minutes, stirring frequently.