Preheat your oven to 400°F (200°C).
In a saucepan over medium heat, melt 2 tablespoons of unsalted butter until bubbling gently. Add in minced garlic, finely chopped onion, and diced celery; cook until softened, about five minutes.
Stir in 2 tablespoons of all-purpose flour and cook it for one minute to form a roux.
Slowly whisk in 1½ cups of seafood stock followed by ½ cup of heavy cream; stir until smooth and allow it to thicken slightly over five to seven minutes before seasoning with Old Bay seasoning, salt, and pepper.
Once your sauce is thickened, fold in ½ pound of shrimp and cook them until they turn pink—approximately two to three minutes—before stirring in chopped cooked lobster meat along with fresh parsley.
In another bowl, whisk together 1 cup of all-purpose flour, baking powder, garlic powder, and salt; then cut in grated cold butter until crumbly before mixing in shredded cheddar cheese and milk until just combined into a sticky dough.