Preheat the oven to 400 degrees.
Melt butter in a saucepan over medium heat. Add the onion and cook for 3-4 minutes. Stir in flour and cook for 1 minute to make a thick paste.
Slowly whisk in chicken broth and heavy cream, stirring until smooth.
Add the chicken, frozen vegetables, fresh thyme, salt, and pepper to taste. Stir and simmer for 2-3 minutes until slightly thickened. Remove from heat.
Roll out the pie crust and cut four circles slightly larger than the ramekins you are using. Set aside.
Divide the filling between 4 small oven-safe ramekins. Brush the rim of the ramekin with the egg wash.
Place the pie crust over the top, pressing around the edges to seal. Cut a small slit in the center for steam to escape. Brush the tops with the egg wash.
Place the ramekins on a baking sheet and bake for 20-25 minutes until the crust is golden brown.
Let the pot pies cool for a few minutes before digging in. Enjoy!