In a large mixing bowl, combine 3 cups flour with 1 teaspoon salt. Add 4 tablespoons shortening and work it into the flour with your fingers until the mixture resembles coarse crumbs.

Gradually add 3/4 cup warm water, mixing until a soft dough forms. Knead for 5 minutes until smooth and elastic. Cover with a damp cloth and let rest for 20 minutes.

While dough rests, heat 2 tablespoons vegetable oil in a skillet over medium heat. Sauté 1 diced onion and 3 minced garlic cloves until softened, about 5 minutes.

Add 2 cups black beans (mashed or refried), 1 teaspoon cumin, 1/2 teaspoon black pepper, and salt to taste. Cook for 5 minutes, stirring occasionally. Remove from heat and let cool slightly.

Stir 1 cup shredded mozzarella cheese into the bean mixture. Set aside.

Divide the dough into 12 equal portions. Roll each portion into a ball, then roll out on a floured surface into a 6-inch circle.

Place 2-3 tablespoons of filling on one half of each circle, leaving a border around the edge. Fold the dough over to create a half-moon shape.

Press the edges firmly to seal, then crimp with a fork for a decorative edge and secure seal.

Heat 2 inches of vegetable oil in a large skillet or deep fryer to 350°F.

Fry empanadas in batches of 3-4, turning once, until golden brown on both sides, about 3-4 minutes per side.

Remove with a slotted spoon and drain on paper towels. Serve hot with salsa, lime wedges, or hot sauce.