In a large pot of salted boiling water, cook the egg noodles according to package instructions until al dente. Drain and set aside.
In a large skillet, heat the olive oil and vegan butter over medium heat. Add the chopped onion and sauté for about 3-4 minutes until softened.
Stir in the minced garlic and sliced mushrooms, cooking for an additional 5-7 minutes or until the mushrooms are tender and have released their moisture.
Pour in the vegetable broth, soy sauce, and stir in the Dijon mustard and paprika. Let it simmer for about 5 minutes, allowing the liquid to reduce slightly.
Reduce the heat to low and stir in the sour cream (or cashew cream), combining everything well. Allow the sauce to warm through, but do not boil. Adjust seasoning with salt and pepper to taste.
Add the cooked noodles to the mushroom sauce, tossing them gently to coat well in the creamy mixture. Allow them to heat together for another 2-3 minutes.
Plate the stroganoff in bowls, garnishing with freshly chopped parsley for a pop of color.