Cook pasta according to package instructions.
Meanwhile, prepare the brown butter mushrooms. Add butter to a saute pan set over medium heat. Allow the butter to melt, swirling the pan sporadically over the next few minutes. The butter will start to turn golden brown. Keep a close eye on it, as it can burn quickly! Once you notice dark brown spots on the bottom of the pan and the butter is slightly foamy, add your mushrooms, tossing to coat them completely.
Reduce heat to medium low, and stir mushrooms every so often to encourage even cooking. Add salt and pepper. After about 5 minutes of cooking, add the garlic and onion. Stir to combine, and continue to cook for another 5-10 minutes, until mushrooms, onion, and garlic are softened.
Once the pasta is done cooking, strain it and add it directly to the pan with the mushrooms. Toss to combine, and sprinkle in 1/2 cup of parmesan cheese.
Serve pasta with additional parmesan, salt, and pepper.