Preheat oven to 400°F. Line two sheet pans with parchment paper.
Melt butter in a large skillet over medium heat. Add hash browns and cook until lightly golden, 6–8 minutes.
Season with garlic powder, onion powder, salt, and pepper. Stir to coat the potatoes evenly.
Lower heat. Stir in condensed soup and sour cream until creamy. Fold in cheddar, green onions, jalapeño, and crushed cornflakes. Warm 1 minute, then let cool 5 minutes.
If using pie dough, roll to 1/8 inch and punch 4–5 inch rounds. If using ready rounds, separate and keep covered.
Spoon 2–3 tablespoons filling onto each round. Brush edges with water, fold over, and press to seal. Crimp with a fork.
Arrange on prepared pans. Brush tops with oil and cut a small vent in each empanada.
Bake 18–22 minutes, until deep golden and crisp. Cool 5 minutes before serving with salsa or sour cream.