1. Preheat your oven to 375°F. Roll out the pie crust and press it into a 9-inch pie pan. Prick the bottom of the crust with a fork and brush with egg wash. Bake for 10 minutes until lightly golden.

2. In a large skillet, melt the butter over medium heat. Add the onion, celery, and red bell pepper, and sauté for 3-4 minutes until softened. Stir in the garlic, Old Bay seasoning, smoked paprika, cayenne (if using), salt, and black pepper. Cook for an additional minute.

3. Add the chopped shrimp and sauté for 2-3 minutes until they turn pink. Remove from heat and set aside.

4. In the same skillet, sprinkle in the all-purpose flour and whisk well. Slowly pour in the heavy cream and milk, whisking constantly until thickened. Stir in the Dijon mustard, lemon zest, white cheddar, and Parmesan cheese until smooth.

5. Return the shrimp mixture to the skillet and gently stir to combine. Transfer the shrimp filling into the pre-baked pie crust.

6. In a small bowl, mix together the panko breadcrumbs, melted butter, Parmesan cheese, and fresh parsley. Sprinkle over the top of the shrimp filling.

7. Bake for 25-30 minutes until golden brown and bubbling. Allow to cool for 5-10 minutes before serving.