Butter a 9x13 inch baking pan and set aside. Preheat the oven to 350 degrees F.
Cook the pasta as per the directions on the pack, drain and set aside.
Bake the pie shell in the oven following the instructions on the package. Set aside while you make the rest of the recipe.
In a large pan, melt the butter and add the flour.
Whisk over a medium heat until the mixture turns slightly golden.
Gradually start to add 1 1/2 cups of the milk whisking all of the time to avoid any lumps.
Add the chicken broth and bring to a simmer.
Once the sauce starts to become slightly thicker, add the salt, pepper and grated Colby cheese.
Whisk until all of the cheese has melted and the sauce is smooth.
Add the frozen veggies and shredded turkey and stir through.
Add the cooked pasta and the remaining 1/2 cup of milk and turn the heat to low while you prepare the topping.
In a bowl crush the baked pie crust with your hands trying to keep it with some larger chunks, you don't want to crush it too finely.
Add the grated white sharp cheddar and toss together.
Transfer the pie filling to the prepared pan and spread out evenly with a spatula.
Sprinkle the pie topping over the filling and bake in the oven for 25 minutes.
Serve at once.