For the pastry, place flour in a mixing bowl and season lightly with salt, about 1/4 teaspoon. Add sage, butter and milk or half-and–half, and combine to form dough.
For the filling, poach chicken in a pot with carrot, celery, onion, bay, herb bundle and salt. Add enough water to just cover the chicken, bring to a gentle boil, reduce heat and simmer about 40 minutes. Remove breast and cool to handle. Strain stock and keep at a low simmer. Remove chicken from bones, discard skin and bones, and pull or chop chicken into bite-sized pieces.