Soak the cashews in enough filtered water to completely cover them while you are making the soup.
Rinse the lentils after checking them to remove any debris (like small pebbles or bits of dried plants). Drain the lentils, then put them in a soup pot with the vegetable stock, pumpkin, curry powder, and smoked salt. Bring to a boil and cook for 30 minutes, or until the lentils are tender. Turn off the heat.
Drain the soaked cashews and put them into your blender with the juice from the lemon half and the salt. Blend, stopping to scrape down the sides as needed. (Use the tamper if you have a Vitamix.) The mixture should end up a very smooth sour cream consistency. If you need to, add a little bit of filtered water to get it to blend.
Scrape out the cashew mixture into a storage bowl. DO NOT WASH THE BLENDER.
Add the soup mixture to the blender and hold down the lid with a kitchen towel. Gradually bring up the speed on the blender so you don't create too much hot steam. Blend until very smooth.
Pour into bowls and add a dollop of the sour cream to each, swirling it in.