Sweet potato empanadas

Name: Sweet potato empanadas
Ingredients: 2 sheets puff pastry ((1 box), defrosted in the refrigerator); 1 lb sweet potatoes ((2 medium sized ones), cooked Note 1); 1 tablespoon olive oil; ½ cup chopped onion ((1 medium sized onion or ½ of a large onion)); 1 teaspoon minced garlic ((4 fat cloves)); 1 tablespoon brown sugar; 1 teaspoon chipotle chili powder (Note 2); ½ teaspoon ground cumin; 1 teaspoon salt; ½ teaspoon black pepper; 1 large egg (beaten with 1 tablespoon water); 1 teaspoon kosher salt (optional)