Cook egg noodles according to package directions until al dente. Drain and set aside.
In a large skillet, heat butter and olive oil over medium-high heat. Add mushrooms in a single layer (work in batches if needed) and cook without stirring for 3-4 minutes until browned. Stir and cook for another 2-3 minutes until golden. Transfer to a bowl.
Reduce heat to medium. Add onion to the skillet and cook, stirring, for 5 minutes until softened. Add garlic and cook for 1 minute.
Sprinkle flour over the onions and stir for 1 minute. Slowly pour in vegetable broth while whisking to avoid lumps. Add Dijon mustard and bring to a simmer, stirring until thickened, about 2 minutes.
Return mushrooms to the skillet. Stir in sour cream and heavy cream. Simmer gently for 2-3 minutes until heated through (do not boil). Season with salt and pepper to taste.
Serve mushroom stroganoff over egg noodles, garnished with fresh parsley.
Tips
For a vegan version, substitute butter with vegan butter, sour cream with cashew cream, and heavy cream with coconut cream.
Serve with a side of steamed green beans or a simple salad.
Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.