Sauté the Base. Set your Instant Pot to 'Sauté' mode. Add the unsalted butter and olive oil. Once the butter melts, add cubed sweet potatoes. Sauté for a few minutes until slightly softened.
Add Broth and Seasonings. Pour in the vegetable broth. Add thyme, bay leaves, salt, and pepper.
Pressure Cook. Seal the Instant Pot and set it to 'Manual' or 'Pressure Cook' mode for 10 minutes.
Puree the Soup. Once cooked, allow a natural pressure release. Remove the bay leaves and use an immersion blender to puree the soup until smooth.
Serve. Ladle into bowls and serve hot. Garnish with a sprinkle of grated Parmesan cheese and serve with a slice of crusty bread.