Begin by bringing a large pot of salted water to a rolling boil. Add the pasta and cook until al dente, about 8-10 minutes. Drain and set aside, reserving some cooking water.

Heat a skillet over medium heat and add butter. Once melted, add the mushrooms, sautéing for 5-7 minutes until golden brown.

Add onion to the skillet and sauté for 3-4 minutes until translucent. Then, add garlic and cook for 1 minute until fragrant.

Pour in the broth and scrap up any browned bits. Let simmer for about 2 minutes.

Reduce heat to low and stir in sour cream and heavy cream until smooth. Add Dijon mustard and let it gently bubble.

Season with black pepper and add the drained pasta. Toss to coat. Heat for 1-2 minutes.

Sprinkle with parsley and serve immediately, optionally with garlic bread or salad.