01 - Heat olive oil and 2 tablespoons butter in a large heavy-bottomed skillet over medium heat until butter melts and foaming subsides.
02 - Add chopped onion and cook, stirring frequently, until translucent and softened, about 3 minutes.
03 - Stir in minced garlic and cook for 1 minute until fragrant, being careful not to brown.
04 - Add sliced mushrooms and thyme. Sauté until mushrooms are golden brown and their liquid has evaporated, approximately 7 minutes.
05 - Stir in Arborio rice and cook for 2 minutes, allowing grains to toast lightly and absorb flavors, stirring constantly.
06 - Pour in white wine, stirring continuously until mostly evaporated and absorbed by the rice.
07 - Add warm broth one ladleful at a time, stirring frequently. Wait until liquid is mostly absorbed before adding more. Continue until rice is creamy and al dente, about 18-20 minutes.
08 - Remove from heat. Stir in remaining 2 tablespoons butter and ½ cup Parmesan cheese until melted and creamy. Season with salt and pepper to taste.
09 - Serve immediately, garnished with additional Parmesan cheese and chopped parsley if desired.