In your 6 quart or larger slow cooker, add carrots, baby potatoes, onion and garlic.
Place the brisket on top, add the seasoning packet plus the extra pickling spices (if using) and pour in the beer.
Cover and cook on low for 8 hours.*
Once cooked, use tongs to remove the brisket to a small, rimmed metal baking sheet. Cover tightly with foil and keep warm on the lowest setting.
Submerge the cabbage into the cooking liquids (if necessary, remove some of the carrots and potatoes -keeep warm in a dish covered tightly with foil) and cook for 1 hour or until the cabbage is fork tender. (the smaller the cabbage the faster it will cook)
Slice the corned beef and serve with mustard (if desired), carrots, potatoes and cabbage.
Top vegetables with butter, salt and pepper and sprinkle with minced parsley. Serve with soft dinner rolls or sliced bread.
*I have never tested this recipe using high heat with a shorter cooking time. Therefore, I cannot tell you with certainty how it will turn out. If you try it, please let me know how it works for you!