Preheat the oven: Set your oven to 375°F (190°C) to prepare for baking the bread bowls. This ensures they will be crispy when serving.
Prepare the bread bowls: Hollow out the large sourdough bread bowls, carefully cutting away the inner bread while leaving a crust-like shell. Brush the insides with 1 tbsp olive oil to enhance flavor. Place them on a baking sheet and bake for 10 minutes, or until they become crisp and golden.
Sauté the aromatics: In a large pot, heat 1 tbsp olive oil and 2 tbsp unsalted butter over medium heat. Add the diced onion and minced garlic, stirring occasionally until the onions become translucent and aromatic, about 5 minutes.
Create the roux: Sprinkle in 2 tbsp all-purpose flour and stir continuously for 1-2 minutes to form a roux, ensuring it's well combined and free of lumps.
Add the broth: Gradually whisk in 4 cups seafood or chicken broth, ensuring no lumps remain. Bring the mixture to a simmer, allowing it to thicken, which should take about 5-7 minutes.
Incorporate the cream: Slowly pour in 1 cup heavy cream, stirring to combine. Then, add 1/2 tsp Old Bay seasoning and 1/4 tsp cayenne pepper (if using) for flavor, simmering for an additional 5 minutes.
Add the seafood: Gently stir in 1/2 lb shrimp, 1/2 lb lump crab meat, and 1/2 lb clams (if using). Cook for 3-5 minutes until the shrimp are just cooked through and warmed. Be careful not to overcook the seafood.
Finish the soup: Remove the pot from heat and stir in 1 tbsp lemon juice and 2 tbsp chopped parsley to brighten the flavors.
Serve: Ladle the rich seafood soup into freshly baked bread bowls, garnishing with additional parsley if desired. Serve immediately, accompanied by pieces of the hollowed-out bread for dipping.