Sauté the chopped onion, green onions, leek, and bell pepper until golden.

In a bowl, mix the sautéed vegetables with the corn.

Dissolve the cornstarch in a few tablespoons of cold milk.

Heat the butter, add the dissolved cornstarch, and then the rest of the milk, stirring until thickened.

Season the white sauce with salt, nutmeg, and black pepper.

Mix the thickened white sauce with the vegetables and corn.

Moisten the edges of the empanada dough rounds with water before shaping.

Fill the dough rounds to form small baskets and place a cube of mozzarella in the center of each.