Place a large pot or dutch oven on the stovetop over medium - high heat.
Add onions, 1 carrot, celery, corned beef, seasoning, and water into the pot. Let it come to a rolling boil, then turn it down to simmer. Cook for 50 minutes per pound, we usually pick up about 4 lbs corned beef so this would be about 3 hours and 20 minutes.
Pull out corned beef and let it sit for 1 full hour. Remove the fixings from the broth (DO NOT GET RID OF THE BROTH) add potatoes, carrots, and cabbage and let it simmer for 25 minutes.
Serve on rye bread with coleslaw, sauerkraut, potatoes, etc