Warm the vegetable broth in a saucepan over low heat before starting. Keeping it warm ensures the rice cooks evenly and absorbs liquid smoothly. Cold broth can shock the rice and slow down the cooking process.
Heat olive oil and butter in a wide pot over medium heat. Add the chopped onion and cook until soft and translucent. Stir in garlic and cook briefly until fragrant, being careful not to let it burn.
Add sliced mushrooms and thyme to the pot and cook until the mushrooms release their moisture. Let them brown slightly for deeper flavor. This step adds that rich, earthy taste I love in mushroom risotto.
Stir the Arborio rice into the pot and cook for about one minute. The rice should be well coated in oil and slightly translucent around the edges. This step helps the rice absorb liquid gradually.
Pour in the white wine and stir until it mostly cooks off. The wine lifts any browned bits from the bottom of the pot and adds brightness. This balance keeps the risotto from tasting heavy.
Begin adding warm broth one ladle at a time, stirring often. Let the rice absorb most of the liquid before adding more. This slow process is what creates the creamy texture.
Once the rice is tender but still slightly firm, remove the pot from heat. Stir in Parmesan cheese, salt, and pepper. The risotto should be creamy and flow gently on the plate.