Preheat oven to 375°F.Heat a skillet and add diced beef fry. Cook until crispy and then remove from the pan using a slotted spoon. Add in onion, carrots (if using) and celery. Sauté for 5-7 minutes, adding oil as necessary. Add the garlic and sauté until fragrant. Add in a splash of the chicken broth and cook for 2-3 minutes.
Sprinkle the flour over the mixture and continue to sauté until the flour starts to take on some color. Add the remaining chicken stock and bring to a simmer, whisking as it cooks to incorporate the flour. Season with salt and pepper. Add chicken and stir to incorporate. Add in the beef bacon and peas. Pour into a pie dish or skillet and cover with puff pastry squares. The pastry squares should overlap the dish by 1”-2” (they will shrink while baking). Brush the puff pastry with egg mixed with 1 tablespoon water.
Bake until puffed and golden, about 30-35 minutes.