1) Put the oil in the Instant Pot and select “Sauté”.
2) Add the onions and cook for about 3 minutes.
3) Add garlic and rosemary and cook for about 1 minute.
4) Stir in the broth, lemon juice, salt, black pepper and mussels.
5) Secure the lid and cook under “Manual” and “High Pressure” for about 5 minutes.
6) Select the “Cancel” and release the pressure quickly.
7) Remove the lid and transfer the mussels into a serving bowl.
8) Top with the cooking liquid and sour cream and serve.