Stuffed Chicken with Pastry Crust

INGREDIENTS

• 6 tablespoons cold butter
• 2 cups all-purpose flour
• 1/2 teaspoon salt
• 1/3 cup water, or more as needed
•  
• 3 skinless, boneless chicken breast halves
• 1 cup shredded White American cheese, divided
• 2 1/2 cups fresh spinach leaves, divided
• 3 tablespoons dried basil
• 3 teaspoons garlic powder
• 3 pinches garlic salt
• 1 beaten egg