1. Prepare the Crust:

1. Preheat oven to 400°F (200°C). Line a sheet pan with parchment paper.
2. In a skillet over medium heat, heat olive oil. Add onion and celery; cook until softened, about 5 minutes. Add garlic and cook 1 minute more.
3. Add chopped shrimp to skillet and cook until pink and just cooked through, about 2-3 minutes. Remove from heat and let cool slightly.
4. In a large bowl, combine cooked shrimp mixture, crab meat, cream cheese, mayonnaise, Dijon mustard, lemon juice, parsley, Parmesan cheese, salt, and pepper. Mix gently until well combined.
5. On a lightly floured surface, roll out each pie crust to about 1/8-inch thickness. Cut out rounds using a 4-inch biscuit cutter or a small bowl as a guide (you should get about 8 rounds).
6. Place about 2 tablespoons of filling in the center of each round. Brush edges with beaten egg. Fold dough over to form a half-moon shape and press edges to seal. Crimp with a fork to ensure a tight seal.
7. Place hand pies on prepared sheet pan. Brush tops with remaining beaten egg and cut a small slit in each pie to allow steam to escape.
8. Bake for 20-25 minutes, or until golden brown and puffed. Let cool on pan for 5 minutes before serving.