Melt 6 tablespoons unsalted butter in a pan, add ½ cup finely chopped onion1 clove garlic minced (if using) and cook, without browning, until softened, about 2 minutes.
Sprinkle 6 tablespoons all-purpose flour and stir to mix with a wooden spoon. Cook over medium heat, stirring constantly, for 3 or 4 minutes, until barely starting to color.
Add 1 cup milk slowly while stirring constantly. Let it come to a boil and remove from the heat.
Add 6 cups corn kernels, ⅓ cup chopped basil, ¼ cup sun-dried tomatoes, ½ teaspoon salt and a large pinch black pepperor to taste. Mix thoroughly and let cool completely. Or better yet, chill it in the fridge for an hour or more.
To assemble:
Preheat the oven to 375ºF (190ºC).
Put 3 or 4 tablespoons of the filling on each dough round. Don't overdo it with the filling or they might burst during baking. If it's your first time, you can do a test run with a few empanadas.
Moisten the edge of the dough lightly with water and close, pressing the dough together. Flute the edges with a fork or your hands and arrange the empanadas on a buttered baking tray.
Bake for 30 minutes or until lightly browned and dry.
Transfer to the serving platter and eat hot or warm.
Notes
Make the dough ahead and freeze the dough discs separated with freezer sheets. Don't freeze without separating or you'll have a hot dough mess impossible to use. Make the white sauce ahead. It keeps in the fridge for a week and frozen for a month.Make sure you close the edges well so the filling doesn't spill during baking. The easiest way is to bind both edges with some water (the dough sticks well) and then press with the tip of a fork creating indentations. It will be sealed.Freeze empanadas: assemble the empanadas and freeze them, unbaked, for a month. To bake, transfer them to a baking tray without defrosting and bake in a 350ºF/180°C oven.For a glossy finish, brush the top of the empanadas with egg mixed with a bit of milk.