Add vegan butter to a saucepan over medium heat. Once it's melted, add chopped onions and cashews. Stir to coat. Cook for 3 to 5 minutes, until the onions are tender. Add chopped garlic and cook for another minute.
Add water and bouillon to the saucepan. Stir to combine. Bring it to a boil and reduce it to a simmer. Simmer for 4 to 5 minutes. Remove from heat and set aside to cool slightly.
Once the broth mixture has cooled, transfer it to a blender. Add vegan cream cheese and vegan parmesan. Pulse in several short bursts. Then use a spatula to scrape down the sides of the blender jar. Then pulse again, increasing the speed until the mixture is smooth.
Pour the alfredo sauce into a glass jar or sealable container. Sprinkle with pepper. The sauce may seem a bit runny at first but it thickens as it cools.
Serve over cooked pasta, on garlic toast, or even as a sauce for pizza.
Keep leftover vegan alfredo sauce in the fridge. It will keep up to 5 days when stored properly.