From Chef Oonagh Williams of Royal Temptations Catering.
1. Remove corned beef from package and place in slow cooker or oven safe casserole dish (Make sure it has a tight-fitting lid; otherwise, the juices evaporate, leaving the meat dry and salty.)
2. Pour the beer and water around the beef. Add the chopped onion, garlic and bay leaves. Mix mustard and brown sugar together and smear over the beef.
3. Cook the meat until tender. For slow cookers, it’s about 6 hours on low for a 6-quart slow cooker. In the oven, cook at 325 degrees for about 3 hours. Remember, every slow cooker and oven varies, so keep an eye on it.
4. About 1 hour before the meat is tender, add sliced carrots, pearl onions and potato chunks. If using a slow cooker, turn it up to high so the vegetables cook through.
5. Remove the tender meat from the casserole and let rest for at least 15 minutes. This also gives you enough time to cook the vegetables longer if they are not tender enough.
6. Add cornstarch/water mixture if the juices need some thickening.
7. Serve slices of corned beef with the potatoes, carrots and onions.
I find most pre-seasoned meats to be far too salty for me, so I remove the beef from the packaging, rinse off and then soak overnight in water to cover in the fridge. When you are ready to cook the beef, remove from water and rinse before placing in the slow cooker or casserole dish.
If you like to serve corned beef with cabbage: Quarter, remove core and finely slice a head of green cabbage. Cook in boiling, lightly salted water for about 8 minutes until only just tender. Drain and return to hot pan with butter and some freshly ground black pepper.