In a small pan, melt 4 Tblsp butter (use margarine if you're cooking vegetarian) and saute 1 cup chopped onion, 2 gloves crushed garlic and 1/3 cup of chopped cashews. Saute until the onions are translucent. Just before it's finished, stir in 1 tsp each thyme, marjoram and basil. Add to the carrots and potatoes.
If you're using a standard blender, puree the soup in small batches until smooth. To avoid accidents, you'll want to make sure the soup is cool before beginning. Trying to blend hot soup is asking for trouble (voice of experience). You'll need to reheat the soup before serving.
If you're using an immersion blender, you can work with the soup while it's still hot (just be careful) or let it cool first. Keep the blender head below the surface to prevent spattering. Blend until the soup is smooth. There may be some small chunks of carrot left, so you might want to run the soup through a colander before serving. It should still be hot enough, but if not, you can reheat it before serving.
Just prior to serving, stir in 1 cup of heavy cream. Garnish with some toasted bread crumbs or panko.