To begin, peel the plantains and cut them into thick slices. Place them in a medium sized pot, add 1 cup of water, and a pinch of salt. Cover and boil over medium heat for about 15 minutes or until the plantains are very soft and tender. This step ensures the plantains will be easy to mash and form into a pliable dough.

Once the plantains are cooked, drain any excess water and transfer them to a large mixing bowl. Using a potato masher or fork, mash the plantains until they form a smooth and sticky dough. Allow the dough to cool slightly to make it easier to handle.

Prepare the filling by mixing sweetened condensed milk or dulce de leche with vanilla extract (if using) in a small bowl. This will add a fragrant sweetness to the filling. Ensure the filling has a thick, spoonable consistency to prevent leakage during frying.

To shape the empanadas, lightly oil your hands to prevent sticking. Take a golf ball sized piece of plantain dough and flatten it into a small disc in the palm of your hand. Aim for a thickness of about 1/4 inch for durability during frying.

Spoon about 1 teaspoon of the filling into the centre of the disc. Carefully fold the dough over the filling to create a half moon shape. Gently pinch the edges together to seal. For added security, press the edges lightly with a fork. Repeat with the remaining dough and filling.

Heat the vegetable oil in a deep skillet or frying pan over medium heat. Test the oil by dropping a small piece of dough into the pan; it should sizzle immediately but not burn. Fry the empanadas in small batches, turning occasionally, until golden brown and crisp, about 2-3 minutes per side.

Remove the empanadas with a slotted spoon and place them on a plate lined with paper towels to drain excess oil. If desired, roll each empanada in granulated sugar while still warm for a delightful sweet coating.

Serve the empanadas warm as a dessert or snack. For an authentic Salvadoran experience, pair them with a hot cup of coffee or atol (a warm, traditional corn based drink). Arrange them on a platter for a beautiful presentation and garnish with a sprinkle of powdered sugar if desired.