Put a large pot of water on to boil. Add about 2 tablespoons of salt to the water.
While waiting for the water to boil, chop your mushrooms, shallots and garlic.
Put the oil in a large saute pan and heat on medium. Once warm, add the shallots and cook about 3 minutes until softened.
Raise the heat to medium-high and add the mushrooms. Heat needs to be fairly high under mushrooms to pull the water out from them and brown them.
Add the herbs plus the white wine, if you’re using at this point.
Your water should be boiling; add the pasta and make sure you don’t overcook it.
Once the mushrooms have been cooking about 4 minutes and are getting browned, add the garlic for an additional minute of two. Be careful not to burn the garlic. If anything is starting to get too brown, use a splash of vegetable broth to prevent any burning or sticking.
Take 3/4 of the cooked mushrooms and place in a high speed blender with 2 cups of the vegetable broth and cashews. The broth is not heated so no worries about blending a hot liquid.
Blend on high, adding more veggie broth as needed until smooth and the desired thickness. The sauce should be fairly thick and very creamy.
Add salt and pepper to taste.
Place the sauce back into the original saute pan to heat.
The pasta should be done about this time. Strain it and add it to the heated sauce.
Top with a dollop of sour cream and serve immediately.