I really love this recipe from Everyday Food magazine (October 2009):
4 Tbspns unsalted butter
1 med. onion diced
1 large carrott diced
1/2 c. flour (plus a bit more for workspace)
coarse salt and group pepper
4 cups low-sodium chicken broth
3 cups cooked chicken cut into 1" cubes
1 cup frozen peas
1 1/2 tspns chopped fresh thyme leaves
1 sheet frozen puff pastry, thawed
1 large egg yolk
1. In a medium saucepan, melt butter over medium. Add onion and carrot and cook until onion softens, about 6 min. Add flour and 1/2 tspn salt; cook, stirring frequently, until mixture is pale golden, has a slightly nutty aroma, and is the texture of cooked oatmeal, about 5 min.
2. Whisking constantly, add broth. Bring to a boil, stirring frequently until mixture thickens, about 8 min. Reduce to a simmer and cook 10 min. Stir in chicken, peas, and thyme; season with salt and pepper. Divide mixture among four 12-ounce baking dishes, refrigerate until room temperature, about 20 min.
3. Preheat oven to 375 degrees. On a lightly floured work surface, roll pastry to an 1/8" thickness. Cut into 4 equal squares, 1" larger than dishes, with the tip of a sharp knife, cut vents into pastry. In a small bowl, lightly beat egg yolk with 1 tspn. water, top pot-pies with pastry and brush with egg wash. Refrigerate 15 min. Bake until pastry is deep golden and juices are bubbling, about 35 min.