Corned beef is beef brisket salt cured, traditionally for preservation. You can find corned beef in the grocery store already cured with a packet of spices. A traditional St. Patrick's Day meal in the US is Corned Beef and Cabbage.
In your instapot, placed sliced onions in the bottom. Place trivet over the onions.; This makes removal of the cooked beef easier. Place corned beef, fat side down on trivet. Sprinkle seasoning packet on the beef. Pour beer and water in the bottom of the instapot being careful not to wash the seasonings off the meat.
Put the lid on the instapot and set it on high pressure for 90 minutes. It will take about 20 minutes to come to pressure. When the 90 minutes is over, allow natural release for 20 minutes and then quick release the rest of the way.
Trim the fat off of the meat then cut in slices against the grain. Serve with steamed cabbage and creamy mashed potatoes.
This recipe I developed about 10 years ago. We ate it on a pretty regular basis served with "sizzled" kielbasa and mashed potatoes. When my daughter was born and was nursing, I stopped making it because it would hurt her little tummy and totally forgot about it. I am excited to bring it out of the vault and add it to meal rotation again. It tastes amazing with sour cream or plain Greek yogurt and mashed potatoes.
Heat olive oil in a large dutch oven over medium heat. Cut onions into large dices. Saute onions in olive oil with 1/2 tsp salt until softened.
Meanwhile, prepare the cabbage. Remove outer leaves from the head of cabbage. Cut into quarters and then cut at an angle to remove the core.
Cut cabbage into 1" slices and add to the dutch oven with the onions. Stir to combine and break up the cabbage. Add 1 tsp salt and 1/4 cup of water. Cover to allow to steam. Cook for 15 minutes. Serve as a side dish.
If you add 1/2 cup of water instead of just the 1/4, there will be a little more liquid goodness when you spoon it over mashed potatoes.