7ouncesall-butter puff pastrydivided into 4 equal rectangles or squares sized to fit your baking dishes, also (see recipe notes)
Preheat oven to 400°F.
Butter 4, 1 ½-cup individual casserole or pie dishes and set aside.
Heat olive oil over medium heat in a medium saucepan. Add onion, lightly sprinkle with salt to sweat liquid and keep from browning; cook and stir 2 to 3 minutes until softened. Add carrots, celery, and potato; cook and stir 2 minutes more. Add broth and sage; bring to boil. Reduce heat and simmer 6 minutes or until vegetables are nearly tender.
Meanwhile, make a roux: heat a small saucepan over medium heat. Add butter. Once butter melts, add flour all at once. Whisk constantly for a minute or two, just to cook out the raw flour taste.
Add cooked turkey and roux to broth mixture and stir to combine; bring to simmer. Cook and stir until thickened, about 3 minutes. Stir in half and half and season to taste with salt and freshly ground black pepper.
Divide mixture evenly between 4 prepared dishes. Arrange dishes on a cookie sheet to catch any splatter. Top each dish with a puff pastry square and transfer to oven.
Bake 25 to 30 minutes, or until pastry is puffy and golden brown. Remove from oven and let cool for 5 minutes before serving.