In a large mixing bowl, combine flour and a pinch of salt. Cut in very cold butter using a pastry cutter until the mixture resembles coarse crumbs. Gradually add chilled water, mixing until a dough forms. Wrap the dough in plastic wrap and refrigerate for 30 minutes.

Peel and cube sweet potatoes, then boil them in salted water for about 15 minutes or until fork-tender. Drain and mash the sweet potatoes in a mixing bowl, then add cream cheese, sugar, cinnamon, and nutmeg. Mix until smooth and creamy.

After the dough has chilled, roll it out on a floured surface to about 1/8-inch thickness. Cut out circles from the dough. Place a spoonful of the filling in the center of each circle, fold and seal the edges.

Preheat the oven to 350°F (175°C) and line a baking sheet with parchment. Arrange filled empanadas on the sheet, brush with egg wash, and bake for 25-30 minutes or until golden brown.

Remove empanadas from the oven and let them cool for 5-10 minutes before serving warm.