Preheat the oven to 425°F. Prepare a muffin tin with non-stick cooking spray.

In a medium saucepan, heat the chicken, vegetables, water, and bouillon over medium heat. Stir to combine and boil for 5 minutes, stirring occasionally, until the chicken is cooked through. Remove from heat and strain the chicken and vegetables, reserving the broth.

In a medium saucepan over medium heat, melt the butter. Whisk in the flour, salt, and pepper. Cook for 1-2 minutes until the mixture begins to brown.

Add milk and reserved chicken broth to the mixture. Continue cooking and stirring until the sauce thickens.

Remove from heat and stir in the reserved chicken and vegetables. Set aside.

On a lightly floured cutting board, unroll one pie crust (leave the other refrigerated until ready to use). Using a 4-inch round cookie cutter, cut out four pieces of dough. Cut out another four pieces using a 3-inch round cookie cutter. Repeat with the second pie crust.

Press the large rounds of dough into the bottom of the prepared muffin tin, ensuring a bit of the dough comes up over the rim of the muffin tin so the top crust can seal to the bottom crust.

Spoon the filling into the pastry and cover with the small rounds. Use a fork to crimp the edges together.

Whisk together the egg and a teaspoon of water. Use a pastry brush to lightly brush the egg wash over the crusts.

Use a knife to cut slits in the top of the pastry so the steam can escape.

Bake for 22-25 minutes until golden brown. Allow to cool for 10-15 minutes, then remove from the pan and serve.