In a food processor pulse flour and salt until combined. Add butter and cream cheese. Pulse until pieces are pea size. Beat 1 egg in a small bowl; beat in cream. With the processor running, drizzle egg and cream mixture throughout the hole in the lid, then add water, 1 Tbsp. at a time as needed, just until dough starts to stick together. Use hands to lightly knead and press dough into 2 balls. Flatten, wrap in wax paper, and chill at least 30 minutes or up to 1 day.
Meanwhile, for filling, blanch 4 cups fresh spinach in boiling water 1 minute, then transfer to an ice bath. Drain spinach, squeezing out as much liquid as possible, then finely chop. In a medium bowl combine spinach, feta, Parmesan, pine nuts (if using), garlic powder, and crushed red pepper, oregano, and nutmeg.
Line a large baking sheet with parchment paper. Roll dough to ⅛-inch thickness. Cut out rounds using 4-inch cutter. For egg wash, in a small bowl beat remaining egg with 1 Tbsp. water. Brush half of the pastry rounds with egg wash, then top with about 1 Tbsp. filling. Fold round in half, pressing edges together. Press edges with the tines of a fork to seal. Arrange on prepared baking sheet and chill 10 to 20 minutes.
Meanwhile, preheat oven to 400°F. Brush tops of hand pies with egg wash and poke a hole in the center of each pie with a skewer or knife. Sprinkle with flaky sea salt. Bake 15 to 17 minutes or until puffed and golden.