Heat vegetable stock in a small pot over low heat - you want the stock to be hot, but you don't want it simmering. Keep the stock warm during the whole process.

In a separate large skillet heat olive oil over medium heat. When the olive oil is hot, add the dice onion and sliced mushrooms to the pan. Saute for 5-7 minutes - you will want the mushrooms to be soft and browned slightly. Season with just a pinch of salt.

Add the butter to the pan and stir until fully melted. Add the rice to the pan and stir to coat in the mushroom and butter mixture. 

Pour the wine into the pan and let it simmer as you stir it into the rice. When the wine is fully evaporated, start pouring small amounts of the vegetable stock from the warm pot into the pan with the rice. I use a soup ladle for this and do one ladle at a time.

Stir the warm stock into the rice and mushrooms in the pan. The pan should be warm enough that the stock simmers lightly. When the stock is fully absorbed by the rice, add another ladle of warm stock into the pan and stir again.

Continue this process until all of the stock is added to the pan with the rice and mushrooms. After about 20 minutes all of the stock should be absorbed by the rice and the rice should be tender. If the rice is not fully tender, you can add some warm water a little bit at a time until the rice is fully cooked.

Remove the pan from the heat and stir in the parmesan cheese and truffle oil. Season with salt to taste and add fresh cracked black pepper on top and serve immediately.