Rinse the corned beef under cold water to remove excess surface salt from the cure, then pat dry. Peel and cut the onion into ½-inch wedges. Scrub the potatoes and cut them into 2-inch chunks, keeping them in a bowl of cold water to prevent browning. Cut the cabbage into 2-inch wedges and trim the carrots, cutting larger ones into 2-inch pieces. Having everything prepped before cooking begins ensures smooth timing throughout the one-pot process.

Place the corned beef in a large pot (at least 8-10 quarts) and add the prepared onion wedges, pickling spice, caraway seeds, and bay leaf. I like to use caraway seeds generously—they really deepen the traditional flavor of the broth and make the whole dish sing. Cover everything with cold water until the beef is submerged by about 2 inches. Bring to a boil over high heat, then reduce to a gentle simmer. Cover partially and cook for 2½ hours until the corned beef is fork-tender, skimming any foam that rises to the surface in the first 10 minutes.

Once the corned beef is tender, carefully remove it from the pot using tongs or a slotted spoon and place it on a cutting board. Tent it loosely with foil to keep it warm while you continue cooking. Strain the cooking liquid through a fine-mesh strainer, discarding the spent onion, spices, and bay leaf, then return the flavorful broth to the pot. Taste the broth and season lightly with salt and pepper if needed—remember the corned beef cure already added plenty of salt to the liquid.

Bring the strained broth to a boil and add the prepared potatoes first—they take longer to cook than the other vegetables. Boil for about 10 minutes, then add the carrots and cabbage. Simmer everything together for 15-20 minutes until the potatoes are fork-tender and the cabbage is just tender but still has a slight bite to it. I prefer my vegetables on the firmer side, so I keep a close eye on them and pull them out as soon as they're done rather than letting them go mushy.

Remove the corned beef from the cutting board and slice it against the grain into ¼-inch thick slices. Arrange the sliced corned beef on a large serving platter or individual plates and surround with the cooked vegetables, ladling some of the flavorful broth over everything. Serve immediately with crusty bread, whole grain mustard, and butter on the side for guests to customize their plates.