Melt the butter over medium heat, add the mushrooms and shallots and cook for about 15 minutes or until tender.
Add the raisins and balsamic vinegar. Cook for another 3 minutes and remove from heat, cool down.
Empanada assembly
To assemble the empanadas, place a spoonful of the mushroom mixture and grated cheese on the center of the empanada discs.
Brush the edges of the empanada discs with the egg whites, this is will help them seal better and keep the filling from leaking while baking .
Fold the empanada discs and seal the edges, use a fork to help seal the empanadas, or use your fingers to twist and curl the edges creating a churito or curl type seal.
Lightly brush the top of the empanadas with the egg yolk; this will give a nice golden glow when they bake.
Chill the empanadas for at least 30 minutes, this will help them seal better and prevent leaks.
Pre-heat the oven to 400 F and bake for 15-20 minutes or until golden.