Press the Saute button on the Instant Pot. Allow it to warm up for 2 minutes. Add the cooking oil.
Add the onion and carrot and saute, stirring often, for 3 minutes. Add the garlic, salt, pepper, rosemary, thyme, and butternut squash. Saute, while stirring, for an additional 3 minutes. Be careful not to burn.
Add the broth to the pot. Stir well, making sure to remove the browned bits from the bottom of the pot.
Seal the lid. Press the Pressure Cook button and set the time to 8 minutes. When done, allow the pot to release the pressure naturally. (If you're in a hurry, you can manually release the pressure),
Using an immersion blender, blend the soup until smooth and silky (about 4 minutes). Serve with any garnish you like: roasted pumpkin seeds, croutons, or a pinch of paprika or nutmeg, if desired.
Notes
You can use frozen store-bought butternut squash in place of a fresh one, if you want.
If you don’t have an Instant Pot, you can make this in the slow cooker or in a pot on the stove. Add all the ingredients to the slow cooker and cook over low heat for 4 hours. On the stove, cook for 30-40 minutes over medium-low heat with the lid on.
For a more creamy soup, add 1/4 cup cream to the blended soup. Do not add the cream before cooking in the Instant Pot or it will curdle.