In a large skillet over medium heat, melt 2 tablespoons of butter. Add the sliced leeks and sauté until they're tender and fragrant, about 5 minutes.

Dice the boneless chicken into bite-sized pieces, then add them to the skillet with the leeks. Pour in 1 cup of low-sodium chicken broth, and simmer until the chicken is cooked through, about 10 minutes.

Stir in 1 cup of heavy cream, seasoning with salt, pepper, and the fresh herbs. Cook until thickened slightly and rich, about 3-5 minutes.

Preheat your oven to 400°F (200°C). Roll out one sheet of puff pastry into a pie dish and pour in the filling. Cover with another sheet of pastry.

Crimp the edges to seal and cut slits on top for steam. Bake for 25-30 minutes until the crust is golden brown.