Prep the seafood. If using fresh shrimp, cook, cool, and chop it into small pieces.
Drain crab well and gently pick through for shells. Pat both dry with paper towels so the dip doesn’t get watery.
Soften the base. In a medium bowl, beat cream cheese until smooth. Stir in sour cream and mayonnaise until fully combined and creamy.
Add flavor. Mix in garlic, Old Bay, black pepper, lemon zest, 1 tablespoon lemon juice, hot sauce (if using), and half the green onions and parsley.
Taste and adjust with a pinch of salt and a bit more lemon juice if needed.
Fold in the seafood. Gently fold in the crab and shrimp so you don’t break up the crab too much. Stir in half the shredded cheese.
Choose your route: baked or chilled. For a hot dip: Preheat oven to 375°F (190°C). Lightly grease a small baking dish.
Spread the mixture in the dish, top with the remaining cheese, and bake for 18–22 minutes until hot and bubbly with light golden edges. Let it sit 5 minutes before serving. Finish with remaining green onions and parsley.
For a cold dip: Cover and chill for at least 1 hour (up to 24).
Sprinkle with remaining cheese, green onions, and parsley just before serving.
Serve. Spoon into a serving bowl and set out with toasted baguette, sturdy crackers, or crisp veggies. A wedge of lemon on the side is a nice touch.