Preheat an oven to 400° F.
In a Dutch oven, over medium heat, melt the butter. Add the onions, celery, mushrooms, carrots and potatoes and cook until onions are softened, about 3-5 minutes. Add the flour and cook, stirring constantly, add nutmeg, 1 to 2 minutes Slowly add the milk cook for another 2 minutes then add stock, stirring until smooth, and bring to a boil. Reduce heat to low. Add the turkey, peas, oregano, parsley, bay leaf and a sprinkling of salt and pepper. Cook until the potatoes and carrots are just tender, about 5 minutes. Remove from the heat and let cool for 5-10 minutes. Remove the bay leaf and discard.
Spoon the mixture into a shallow casserole dish (like a lasagna pan). Roll out the puff pastry and place over filling, pressing or pinching against the edge of the pan. Brush the puff pastry with the egg mixture. Bake until the pastry is puffed and golden brown, about 20 to 25 minutes. Let rest for 5 minutes before serving.
“ ”