In a skillet, heat olive oil. Sauté the garlic, onions and shallots for five minutes or so before adding the mushrooms. Season with salt and pepper. Cook the mushrooms for another five minutes or so. Melt the butter into the mixture and sprinkle the flour onto the mushrooms. The flour will form a paste. Gradually add the milk and stir until well combine. Add the parmesan cheese and spinach and mix well. Cool the mixture before crimping.
On a work surface, lay out several empanada wrappers at a time. Place a heaping tablespoon of filling into the center of the wrapper and fold in half. Crimp the edges using a fork or by twisting the dough together as you would when pinching the edges of pie dough. Repeat until all the filling is used. Place on a parchment paper lined baking dishing and freeze for two hours before transferring to an airtight freezer bag or container.
To cook, pre-heat an oven to 400 degrees. Bake frozen for approximately 20 minutes until golden and cooked through. If cooking before freezing, you will need less time.