Combine stock, potatoes, garlic, salt, and black pepper in the bowl of a pressure cooker (any size will work, but be sure the ingredients are below the fill line) or slow cooker.
Close and lock the lid.
Set the pressure cook / manual setting on high for 5 minutes. (If using the slow cooker, slow cook on low for 6 to 8 hrs or high for 3 to 4 hrs.)
Allow the pressure to release naturally for at least 10 minutes.
Add sour cream and blend until smooth using an immersion blender or standing blender (be extra careful when blending hot liquids).
Taste the soup and season with some more salt and / or black pepper.
Serve immediately or refrigerate for up to 3 days before serving (see note below for instructions on reheating).
Finish by topping each bowl with your favorite toppings!