01 - Warm olive oil and 1 tablespoon butter in a large heavy skillet or Dutch oven over medium heat.
02 - Add diced onion and sauté, stirring frequently, until softened and translucent, approximately 4 minutes.
03 - Incorporate minced garlic and cook for 1 minute until fragrant.
04 - Add sliced mushrooms and thyme leaves; cook while stirring occasionally until mushrooms release moisture and begin to brown, about 7 minutes.
05 - Stir in Arborio rice, toasting for 1 to 2 minutes until grains are translucent at edges.
06 - Pour in white wine and stir constantly until nearly fully absorbed.
07 - Gradually add warm vegetable stock one ladle at a time, stirring frequently and allowing each addition to absorb before adding more; continue until rice reaches creamy, al dente texture, approximately 20 to 25 minutes.
08 - Remove from heat, then stir in Parmesan cheese and remaining tablespoon of butter; season with salt and black pepper to taste.
09 - Plate immediately, garnishing with fresh thyme sprigs if desired.