Add the butter to a dutch oven over medium heat and melt.

Add the onions, potatoes, peas, and carrots to the butter and stir well. Cook over medium heat, stirring occasionally, for 5 minutes.

Add the flour to the vegetables and stir to combine.

Whisk in the chicken broth and milk. Bring to a boil, reduce to a simmer, and cook for 15 minutes or until potatoes are tender.

While soup is simmering, preheat oven to 400 degrees. 

Roll out the pie crust. Whisk together the egg and water and brush over the pie crust.

Sprinkle with salt and cut into small squares for crackers.

Bake on a large baking sheet for 8-10 minutes or until golden brown. 

When potatoes are tender, add the chicken, corn, salt, and pepper to the soup and continue cooking until warmed through.

Serve soup with pie crust crackers on top.