Using pressure cooker, pour about 3 tablespoons cooking oil, heat on high heat, and sear the chuck roast. Remove meat, install bottom rack, and replace meat. Add chopped onions on top, and add 3/4 cup water. Install pressure cover and on high heat, release the steam from the cooker. Install pressure weight and, on high heat, bring to 15 lbs. cooking pressure. Lower heat to medium (to hold 15 lbs. pressure on pressure weight), and cook 35 minutes. Remove and cool under cold water until pressure weight returns to normal. Remove cover, remove meat and rack, and add 1 cup water with 3 tablespoons flour for thickened gravy. Enjoy!