Preheat oven to 400°F (200°C).
In a saucepan over medium heat, melt butter. Add garlic, onion, and celery; cook until softened, about 5 minutes.
Stir in flour and cook for 1 minute to form a roux.
Slowly whisk in seafood stock and cream. Simmer 5–7 minutes until thickened.
Season with Old Bay, salt, and pepper.
Add shrimp and cook 2–3 minutes until just pink. Stir in lobster and parsley, then remove from heat.
In a bowl, mix flour, baking powder, garlic powder, and salt for the biscuit topping.
Cut in cold butter until crumbly, then stir in cheddar and herbs.
Add milk and gently mix until just combined.
Spoon filling into ramekins or a baking dish and drop biscuit dough over the top.
Bake 20–25 minutes until biscuits are golden and cooked through.
Rest 5–10 minutes before serving this Shrimp & Lobster Cheddar Bay Biscuit Pot Pie.