Peel and cut the onions into quarters and place in the bottom of the Instant Pot.
Place the corned beef, fat side down, on top of the onion, then add the crushed garlic and beef broth.
Add the potatoes and carrots.
Sprinkle over the spices.
Place the lid on the Instant Pot and into position. Ensure that the valve is sealed. Pressure cook on high for 70 minutes.
When finished cooking, open the valve to quickly release the steam.
When done, remove the lid. Take out the potatoes and carrots and place in a bowl and cover with foil.
Add the cabbage and beans. Replace the lid, close the valve and select High pressure and cook for 2 minutes.
When done, open the valve to release the pressure.
When finished, remove the lid and take out the corned beef.
Remove the rest of the vegetables and cover to keep warm.
Cut up the corned beef against the grain into slices.
Serve with the vegetables and gravy.
Gravy
Remove about 2 cups of the liquid left over from the Instant Pot and place in a saucepan or microwaveable jug.
Add the cornflour and whisk through making sure there are no lumps.
Cook over medium heat until it boils, then simmer for 2 minutes until it thickens. If using the microwave, heat for 1 minute, then stir and repeat in 30 seconds bursts until thickened.