Switch on your instant pot and press sauté (normal). Add the butter. When it melts, add the onions and garlic. Sauté for 2 minutes until the onions soften.
Crumble the bouillon cubes by hand and add these along with ground spices (cinnamon, nutmeg, black pepper) and salt. Sauté for 1-2 minutes.
Add the cubed sweet potato and roast it with a wooden spoon for 10 minutes on medium heat. Add a few splashes of broth if you find the sweet potato sticking to the bottom. Deglaze the pot in the end (deglazing means to scrape the bottom of the pot to dislodge stuck bits of food. A little liquid, in this case, broth, helps to loosen the food). Cancel the sauté function.
Add the vegetable broth and mix well. Secure the lid, press the pressure cooking button and adjust to high. Make sure the steam release handle is on 'sealing' and set the timer to 3 minutes.
When the timer beeps, release pressure immediately (Quick Pressure Release or QPR) by turning the steam release handle to 'venting' and open the pot. Tip in the can of rinsed and drained butter beans.
Using an immersion blender (if you have one), blend the contents of the pot to a puree like consistency. If you don’t have an immersion blender, wait for the soup to cool down a bit, then blend it in your regular blender in batches.
The soup will be quite thick, so add a cup (or more) of hot water and stir. Press sauté again, stir the soup for a minute or two to make it smooth again, then cancel. Sprinkle extra cinnamon and nutmeg on top and ladle it out in pretty bowls. Your sweet potato soup with butter beans is ready to be served!