Put the pasta on to cook according to the package instructions. When it's cooked, drain and cover. If it starts to stick together at all, add a little olive oil and toss it with the pasta.
While the pasta is cooking you can start on your sauce.
Add butter to a pot on medium heat and let it melt.
Add chopped onions and sauté until the onions are softened.
Add the crushed garlic and sauté with the onions.
Then add in the sliced mushrooms and sauté until the mushrooms are softened.
Add all purpose flour and stir in with the mushrooms and sauté for 1 minute.
Then add in the vegetable stock and stir in until combined.
Now add soy sauce and dijon mustard and stir in. Cook for 4-5 minutes until the sauce is thickened and reduced.
Add sour cream and stir in. Simmer for a few more minutes until thickened.
Add the cooked pasta and stir in until well mixed. Add salt and pepper to taste.
Serve it topped with fresh chopped parsley and a sprinkle of ground black pepper. Freshly grated parmesan cheese on top is also delicious.