Preheat and prep: Heat your oven to 375°F (190°C).
Lightly grease a small baking dish (about 1-quart capacity). Set the cream cheese on the counter to soften.
Quick-cook the shrimp: Warm a skillet over medium heat with the butter and oil. Add the shallot and cook 2 minutes until soft.
Stir in garlic for 30 seconds. Add the chopped shrimp with a pinch of salt and pepper and cook 2–3 minutes until just opaque. Remove from heat and let cool slightly.
Mix the creamy base: In a large bowl, beat the cream cheese until smooth.
Fold in sour cream and mayonnaise until blended. Add mozzarella, 1/3 cup parmesan, Old Bay, smoked paprika, cayenne (if using), lemon zest, and lemon juice. Taste and season with a little salt and pepper.
Fold in seafood and herbs: Gently fold in the crab, cooked shrimp, green onions, and parsley or dill.
Try not to break up the crab too much; you want nice flakes.
Transfer and top: Spoon the mixture into the baking dish, smoothing the top. Sprinkle with a light shower of extra parmesan for browning.
Bake: Bake 18–22 minutes, until hot and bubbling at the edges and lightly golden on top. If you want deeper color, broil for 1–2 minutes—watch closely.
Finish and serve: Let it rest 5 minutes.
Add a few dashes of hot sauce if you like a kick. Serve warm with toasted baguette slices, crackers, or fresh veggies.