In a large cooking pot, boil broth, chicken, carrots, potatoes, and peas until veggies are tender.Mix cornstarch with water until smooth.Stir mixture into the broth/veggies, cooking for about one minute on the stove to help the mixture thicken.Pour contents into a 9x13 inch baking dish.In a separate bowl, stir together milk, mayo, and flour.Spread mixture over the veggies in the baking dish.Bake in a 350° oven for about 45 minutes or until the crust is golden brown.