Press sauté (norma) and add the butter. When the butter melts, add the garlic and onions and sauté for 1 minute.
Add the rest of the vegetables, salt and pepper. Pour in the vegetable broth too.
Cancel sauté and lock the lid. Make sure the steam release vent is on 'sealing'. Press the pressure cooker button (high) and set the timer to 6 minutes. When the timer beeps, wait for 5 minutes and release the pressure. Remove the lid.
Using an immersion blender, puree the soup until it is smooth. Serve hot.
Cooking (Stovetop)
Put a large saucepan on medium heat and add the butter. When the butter melts, add the garlic and onions and sauté for 1 minute.
Add the rest of the vegetables, salt and pepper. Pour in the vegetable broth too.
Allow the soup to come to a boil. Lower the heat and cook until the veggies soften completely (about 25-30 minutes).
Using an immersion blender, puree the vegetables in the liquid until thick and smooth. Serve hot.
Notes
If you don't have an immersion blender, use your regular blender. Make sure the soup is not hot though. You might have to blend it in two batches.
Serve the soup with some warm bread.
For more serving suggestions and storage, look at the body of the post.
To make the soup vegan or dairy-free, swap the butter for the cooking oil of your choice.