Heat chicken broth in a medium saucepan and keep warm over low heat throughout cooking.
In a large skillet, heat 2 tablespoons olive oil over medium-high heat and sauté mushrooms until golden brown, about 5 minutes, then season with salt and set aside.
In the same skillet, add remaining 1 tablespoon olive oil and cook onion until softened, about 3 minutes, then add arborio rice and stir for 1 minute until lightly toasted.
Pour in white wine and stir until absorbed, then begin adding warm broth one ladle at a time, stirring frequently and waiting until each addition is absorbed before adding more.
Continue adding broth and stirring for about 20 minutes until rice is creamy and tender but still has a slight bite.
Remove from heat and stir in cooked mushrooms, Parmesan cheese, cold butter, and truffle oil until creamy and well combined.
Season with salt and pepper to taste, and serve immediately garnished with fresh thyme and extra Parmesan if desired.