1. Trim excess fat from the lamb shanks and season with salt and pepper. 
2. Heat the oil in the PC. Add the shanks and brown on all sides. (You can do this in a separate pan if you like).
3. When the shanks are almost completely browned, add the garlic cloves and cook until they are lightly browned but not burned.
4. Add the stock, port, tomato paste, and rosemary, stirring so the tomato paste dissolves.
5. Close the PC and bring up to full pressure.
6. Reduce heat to stabilize pressure and cook for 30 minutes.
7. Remove PC from heat and let pressure release naturally.
8. Remove the lamb shanks.
9. Return pan to heat and boil the liquid, uncovered, for 5 minutes to reduce and thicken the sauce.
10. Whisk in the butter, then add the vinegar.
11. Serve the sauce over the lamb.

Serves 2. Source: recipezaar.com

Note from JB: I bought my first pressure cooker around Christmas and I LOVE it! You could also cook the shanks in the crock pot all day, or cook them for two hours on 375 in the oven.