Cut the beef brisket into approx 4 large pieces. Season lightly with salt and pepper.

Add the oil to the inner pot of the Instant Pot (IP) and switch it on. Press the Saute button.

When the oil is hot, brown the pieces of meat in batches removing to a plate when done.

Add the chopped onions to the IP and stir, scraping up the browned bits from the bottom of the pot. Cook the onions until they're starting to brown and soften.

Add the beef stock to the pot and stir well. Return the meat to the pot, adding more stock if necessary so that the meat is almost covered. Add a little salt (if using low salt stock) and freshly ground black pepper.

Bring to the boil, then press the Keep Warm/Cancel button.

Lock the IP lid in place, making sure the lever is pointing to Sealing and NOT Venting. Press the Manual button and use the +/- keys to set the time at 60 minutes.

After the time is up, turn off the IP and leave for the pressure to release naturally. Switch to Venting, then carefully remove the lid.

Carefully remove the pieces of brisket, slice and serve it with the cooking liquor or proceed with your chosen recipe.