Melt the butter over medium heat, add the diced onions and cook for about 5 minutes or until soft and translucent.
Add the asparagus and cook for about 5 minutes.
Add the fava beans and cook for about 3 minutes.
Add the peas and cook for another 3-5 minutes. Add salt and pepper to taste. Let the vegetables cool down slightly.
Mix the vegetables with goat cheese and fresh thyme, save the filling until ready to assemble the empanadas.
Empanada assembly
To assemble the empanadas, place a spoonful of the asparagus, fava bean, peas and goat cheese mix on the center of each empanada disc.
If needed, brush the edges of the empanada discs with the egg white or water, this is will help them seal better and keep the filling from leaking while baking .
Fold the empanada discs and seal the edges. You can either use a fork to help seal the empanadas, or use your fingers to twist and curl the edges or to make a repulgue or curled seal for the empanadas.
Brush the empanadas with the egg wash; this will give them a nice golden glow when they bake.
If you have time, 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.