Preheat the oven to 375 degrees F.
In a large bowl, beat the egg whites into stiff peaks.
Fold in the mix of mozzarella cheese, basil chiffonade, sun-dried tomatoes, salt, and optionally, the dried basil (if using).
Use either homemade dough, rolled (or cut) into discs, or store bought discs, and place 2 tablespoons of the empanada filling into the middle of the dough.
Wet the edges of the dough with a little water and fold over into a half-moon crescent.
Either use a fork to crimp the edges shut (basic) or use the ‘repulgue’ technique to fold the empanada dough (this is how these empanadas were photographed).
Place onto a parchment paper lined baking sheet.
Mix egg yolk with 1 tablespoon of water. Brush empanadas with egg wash.
Bake for 25 minutes or until golden brown on the outside.
Let empanadas cool for five minutes and serve with balsamic chimichurri.