Salt and pepper ribs on all sides and let sit for 5-10 minutes. Heat olive oil in bottom of pressure cooker pot to shimmering and brown ribs on all sides. Remove to a plate.
Saute onions and garlic in drippings. Add all remaining ingredients and bring to a boil, boiling for 8-10 minutes or until liquid is reduced by half.
Nestle ribs back in the pot and seal. Bring to high pressure and cook for 40 minutes. Carefully release pressure and serve over mashed potatoes with jus on top.