Chop the onions and garlic. This can be a pretty rough chop as we’re going to blend them later, so it doesn’t have to be super precise here.
Cook the onions and garlic in a medium pot over medium/high heat for 4-5 minutes. Add the tomatoes and their juices, stock, cashews, and cayenne if using. Cook another 2-3 minutes. Then combine everything in a blender and puree until smooth. Taste and add salt and pepper as needed.
Notes
Normally, I recommend either blending your soup in a good blender OR using an immersion blender. But for this particular recipe, I find that a good blender works best as it does a better job at making sure the cashews really get ground up in the mix.That being said, if all you have is an immersion blender, I would still make this soup because it’s still SO yummy. But I just wanted to note that a blender may be best here.