The puff pastry crust isn’t the only secret to the success of this turkey pot pie recipe. For the velvety sauce, you’ll need an ingredient that might be even less expected: American cheese. When combined with flour and water (you could use chicken stock or turkey broth, but you really don’t need to), the superior meltability of American cheese creates a lush no-roux gravy that clings to every part of the pot pie filling.
As for that filling, we start by roasting a boneless turkey breast, but you could certainly swap it for 1½–2 lb. of leftover turkey from a holiday meal (or even a shredded rotisserie chicken). We also call for 20 oz. of frozen vegetables. If you’d rather pick and choose (or use up more Thanksgiving leftovers), aim for about 4 cups frozen peas, sautéed green beans, melted leeks, or whatever vegetables you like.
Have your egg wash ready to gloss the top of the puff pastry sheet as soon as you lay it on the warm filling—this is not the time to wait around. You want the pastry dough to go into the oven as cold as possible so that it puffs. Leaving it too long over the hot filling will allow the butter to melt out, resulting in a dense pastry. Place your casserole dish on a rimmed baking sheet to catch any burbling drips and to make it easier to move in and out of the oven without marring the crust.
