In a large pot, heat the olive oil over medium high heat. Add the onion and cook for 5 minutes, stirring frequently, until it starts to soften and brown, then add the garlic and sage.
Once the garlic has had a minute or two to be mixed into the onions and get nice and warm, add the chopped potatoes and just enough broth to barely cover the potatoes, about 2-3 cups.
Next, add in the chopped cauliflower, give everything a quick mix, then cover the pot and reduce to medium heat. Let it bubble away for 10-15 minutes until the potatoes and cauliflower are nice and soft.
Add in the spinach next, and mix it in so the spinach just starts to wilt. Squeeze in the lemon, making sure not to let any lemon seeds fall into the pot. Season with salt if you like.
Transfer the soup to your blender with a big ladle and blend it in batches, storing the blended soup in a large bowl while you’re getting the next batch from the pot. Once it’s all blended, return all the soup to the pot and heat it through, stirring and tasting for salt and pepper. Add more as needed. Serve your spinach potato soup piping hot, with nutritional yeast sprinkled on top if you like! Feel the love.