Mix flour and salt; cut in cold butter until crumbly.
Add egg, cold water, and vinegar; form shaggy dough.
Knead gently, wrap, and chill for 30 minutes.
Roast sweet potatoes at 400°F for 20–25 minutes.
Sauté onion, garlic, and spices; add black beans.
Combine roasted sweet potatoes, beans, cilantro, lime juice, and corn.
Roll dough, fill with 2–3 tablespoon filling, fold, and seal edges.
Brush with egg wash and bake at 375°F for 25–30 minutes until golden.
Cool for 5 minutes before serving.