Preheat the oven to 450°F. Spray a large baking sheet with non-stick cooking spray and set aside.

In a medium saucepan, melt butter over medium heat. Add diced onions and sauté until translucent (3-4 minutes).

Add flour, salt, and pepper. Cook, stirring constantly, until the mixture begins to brown (3-4 minutes).

Slowly whisk in chicken broth and milk, stirring constantly until smooth. Cook until it bubbles and thickens (about 5 minutes). Remove from heat.

Stir in cream cheese, frozen vegetables, and diced chicken until evenly combined.

Unroll pie crusts on a floured surface. Use a bowl (about 5.5-inch diameter) to cut out circles. Gather scraps and reroll to cut more circles if needed.

Beat egg yolks with water to make an egg wash.

Place three crust circles on a plate or parchment paper. Fill each with about 3 tablespoons of filling in the center.

Brush egg wash around the edges, fold in half to shape a crescent, and crimp edges to seal.

Brush the top with egg wash and poke a few holes with a fork.

Place pies on the prepared baking sheet and repeat until all are assembled.

Bake for 10-12 minutes until golden brown and crisp.