Thaw chicken breasts in refrigerator overnight. Remove from refrigerator, pat dry with paper towels, and dice into 1” cubes.

Season with salt, pepper, garlic, and onion powder. Toss until thoroughly coated and bring to room temperature on countertop.

In a large cast-iron pan, add vegetable oil and bring to medium-high heat, sauté diced chicken breasts about 4 to 5 minutes until chicken is cooked through and golden brown

Reduce pan to medium heat and add 2 tablespoons unsalted butter and onions to pan. Sauté until lightly browned – about 1 minute.

Add thawed vegetables to pan, a pinch of salt and pepper, and sauté about 90 seconds until warmed throughout and tender. Remove all contents from pan.

Add 4 tablespoons unsalted butter and 1/2 cup flour and whisk on medium heat until blond roux forms and clumps are gone – about 1 minute.

Add chicken stock, milk, and heavy cream, a pinch of salt and pepper, Worcestershire sauce, and hot sauce and bring to a boil and thickened – about 2 to 3 minutes.

Once sauce thickens, whisk in cheddar cheese until fully incorporated, fold back in cooked chicken and sautéed vegetables and reduce to medium heat. Cook for another 3 to 4 minutes and season to taste with salt and pepper.

Pour contents into a large bowl and place uncovered into refrigerator for 2 to 3 hours until solidified and cold.

Once pot pie mixture is cold, remove the 4 frozen puff pastry sheets from freezer and place on floured surface for about 40 minutes until malleable. Unfold sheets and preheat oven to 400F.

Cut each pastry sheet in half, width-side, yielding 8 puff pastry squares, brush egg wash was on all four sides of puff pastry squares and spoon about 1/4 cup of pot pie mixture in the center of each puff pastry square.

Fold the longer side of the puff pastry over the pot pie filling in each square, and seal with a fork on all sides except the folded side.

Place the squares on 2 parchment-lined full sheet trays, 4 puff pastry squares on each sheet tray and brush all over the top areas of the puff pastry with egg wash. Place in preheated oven and bake until golden brown and crispy exterior – about 15 to 18 minutes.