Heat the oven to 425°F. Coat all 12 cups of a standard muffin pan with nonstick cooking spray so the pastry shells release more easily after baking.

In a medium bowl, combine the condensed cream of chicken soup, milk, dried thyme, frozen mixed vegetables, and cooked chicken. Stir until the chicken and vegetables are evenly distributed through the creamy mixture.

Unroll the two refrigerated pie crusts. Cut 12 rounds large enough to line the muffin cups, then gently press each round into a cup without stretching the dough too thin.

Spoon the chicken mixture evenly into the pastry shells. Do not overfill; leave a little space around each rim so the filling does not boil over and the tops can be sealed.

Cut additional pastry rounds or small decorative shapes for the tops. Place one over each filled shell, pinch or crimp the edges to seal, and cut a small slit in every top to let steam escape.

If using the optional egg wash, brush the tops lightly with the beaten egg and water. This gives the crust a glossy, golden finish as it bakes.

Bake for 15–20 minutes, or until the pastry is golden brown and the filling is hot and bubbling. Keep an eye on the pies near the end of baking because oven temperatures and crust thickness can vary.

Let the mini pies stand in the muffin pan for about 5 minutes before removing them. This brief rest helps the filling settle and makes the pies easier to lift without breaking the crust.