Heat the oil and 6 tablespoons of the butter in large saute pan over medium-high heat. Add the celery, onions, curry powder and a large pinch of salt and cook until the vegetables are soft and the onions turn translucent, about 10 minutes. Add the garlic and saute for 1 minute, then stir in the peas and carrots. Add the flour and cook, stirring constantly, about 2 minutes. Slowly add the chicken broth and milk, whisking to remove any flour lumps. Bring to a simmer and cook until thickened, about 5 minutes. Season with salt and pepper. Add the chicken and stir to combine.
Pour the curry chicken into four 10-ounce ramekins or gratin-style bowls.
Lightly dust a clean work surface with flour. Roll the pie crust large enough to cut 4 circles to fit over the ramekins. Lightly brush the edges of the ramekins with the egg wash. Place the pie crust over the top of the curry chicken, pressing to seal along the edges. Using a sharp paring knife, create a few slits in the top of the pies. Brush the top of the crust with the egg wash.
Bake until the crust is a deep golden brown and the pot pies are bubbly, about 30 minutes. Let cool slightly before serving. Top with pats of the remaining 2 tablespoons butter right before serving.