Preheat the oven to 400℉/205℃.
Thaw the puff pastry in the fridge, then roll it out so it's slightly thinner (keeping it in a square shape).
1 sheet puff pastry
Add the cast iron skillet over medium heat, then add the olive oil and butter.
2 tablespoons extra virgin olive oil, 2 tablespoons butter
Saute onion, garlic, and herbs, stirring occasionally, until softened and translucent. Add the potatoes and cook for about thre minutes.
1 medium yellow onion, 2 large garlic cloves, 3 stalks fresh parsley, 3 stalks fresh thyme, 1 smalls stalk fresh rosemary, 1 large potato
Add the mixed vegetables and salt and pepper and stir, allow it to heat up for about two minutes.
12 oz frozen mixed vegetables, 1 teaspoon kosher salt, ½ teaspoon cracked black pepper
Add the Worcestershire and flour and toss to coat, then cook for 1 minute.
2 teaspoons worcestershire or soy sauce, ¼ cup all-purpose flour
While stirring, slowly drizzle in the stock, continue to stir as it thickens. Allow the gravy to bubble for a few minutes, stirring occassioanlly.
2 cups turkey or chicken stock
Stir in the heavy cream and bring to a simmer.
¼ cup heavy whipping cream
Add in the turkey pieces and mix. Allow it to simmer for a bit if it needs to thicken further, otherwise, remove it from the heat and allow it to cool for about 15 minutes.
2 cups leftover roasted turkey
Roll out the puff pastry evenly, then place it on top of the filling, allowing it to hang over the edges.
Whisk an egg and brush on top of the pastry.
1 egg
Add two large slits (~2 inches) into the top of the pastry to help steam release.
Bake in the center rack of the oven 20-30 mins until golden brown and bubbling. If the pastry in the center still looks raw, continue baking for a few more minutes at a time. Lightly tent the pastry with foil if it is browning too quickly.