Cook the black bean pasta according the instructions on the package. But subtract 1 to 2 minutes from the recommended cooking time.
Making the Sauce
Dice the onions, chop the garlic, and slice the mushrooms (or buy pre-sliced to save some time).
Use a large skillet with a lid. Heat the olive oil. Once the oil is hot begin to sauté onions and garlic over medium-low heat until the onions become soft (about 5 minutes).
Add mushrooms and 1 cup of vegetable broth. Put the lid on the skillet. This will trap the heat and cook your mushrooms faster. Keep the heat on a medium-low simmer for another 10-15 minutes or until the mushrooms are soft.
Once the mushrooms have cooked, add dijon mustard, salt and pepper. Allow the flavors to marinate. Finally add sour cream to the mushroom sauce.
Add your cooked black bean pasta to the skillet and allow them to simmer with the mushroom sauce sauce for 2-3 minutes.