Brown the sausage. Heat the pot over medium-high. Add sliced sausage and brown until edges caramelize (3–5 minutes). Remove to a plate.
Sauté aromatics. In the rendered fat, add onion and smashed garlic. Sauté 2–3 minutes until glossy. Stir in Old Bay or smoked paprika so the spice blooms.
Add potatoes & stock. Toss in halved potatoes, pour in stock and bring to a simmer. Cook 12–15 minutes until potatoes are just tender (not falling apart).
Return sausage; add corn & cabbage. Return the browned sausage, then stir in corn and the cabbage quarters. Simmer 6–8 minutes — cabbage should be bright and fork-tender, not mushy.
If using shrimp: add in the final 3–4 minutes so they just turn opaque.
Finish. Turn off heat. Stir in butter and lemon juice. Season to taste with salt and pepper, sprinkle chopped parsley, and transfer to a big tray or butcher paper for family-style service. Drizzle extra broth as desired.