Prepare the Dough : In a mixing bowl, combine flour and salt. Add cubed butter and use your fingers to rub it into the flour until it resembles coarse crumbs. Gradually add ice-cold water, mixing gently until the dough comes together. Wrap in plastic and refrigerate for 30 minutes.

Cook the Filling : Sauté diced chicken in olive oil until cooked through. Remove and set aside. In the same pan, soften onions, garlic, carrots, and celery over medium heat. Return the chicken to the pan and stir in cream sauce or chicken broth mixture. Season generously and simmer until thickened.

Assemble the Pastries : Roll out the chilled dough thinly and cut into circles or squares. Place a spoonful of filling onto each piece, brush edges with beaten egg, and seal tightly by folding over or crimping with a fork. Brush tops with egg wash.

Bake : Preheat oven to 200°C (400°F). Place pastries on a baking sheet lined with parchment paper and bake for 20–25 minutes, or until golden brown.