Heat the broth in a saucepan over low heat until just simmering. Keep warm throughout cooking.
In your main pan, melt the butter with a splash of olive oil over medium heat. Once melted, add the finely chopped onion and cook gently, stirring frequently, until translucent and fragrant, about 3-4 minutes.
Add the minced garlic to the pan, stirring until fragrant, about 30 seconds. Then, toss in the sliced mushrooms, cooking until they release their juices and turn golden-brown, around 8-10 minutes. The aroma should deepen, and the mushrooms should look shriveled and caramelized.
Stir in the arborio rice, coating each grain with the butter and mushroom mixture. Cook for 2-3 minutes until the rice becomes slightly translucent at the edges, releasing a nutty aroma.
Begin adding the warm broth a ladleful at a time, stirring constantly. Wait until the liquid is mostly absorbed before adding more. Maintain a gentle simmer and continue this process for about 18-20 minutes, or until the rice is tender but still has a slight bite and the mixture is creamy.
Once the rice is cooked to your liking, remove the pan from heat. Stir in the grated Parmesan cheese and a pinch of salt and pepper. Let the risotto rest for a minute to settle and thicken slightly.
Serve the risotto immediately, garnished with chopped fresh parsley for a bright, herbal finish. The dish should be velvety, with bits of mushrooms evenly distributed and a fragrant, earthy aroma.
