Prepare veloute sauce in advance. Blanch celery, carrots, and snow peas separately until al-dente. Shock in ice water, drain and set aside. Heat the butter in saucepan. Add the onions and cook until translucent, about 3 minutes. Add the celery, carrots, snow peas and chicken. Cook until heated thoroughly. Adjust seasoning, to taste, with salt and black pepper. Add optional herbs at this point. Divide vegetable and chicken mixture between the 4 souffle dishes. Add heated veloute to cover. Top each souffle with a 5 1/2-inch piece of pie dough (just enough to crimp over the edge of the souffle). Brush lightly with egg wash.
Preheat the oven to 350 degrees F. Cut out duck shapes with cookie cutter and place cutout on top of pastry. Brush with egg wash. Bake until cooked through and the crust is golden brown, about 10 to 15 minutes. Serve immediately.
In a saucepan, melt the butter over medium heat. Add the flour and stir. Cook, stirring constantly, until the mixture bubbles and achieves the consistency of pancake batter. Slowly whisk in the chicken stock. Bring to a simmer and cook for 10 to 15 minutes. Season, to taste, with salt and pepper.