In a large pot add water and salt for pasta. Bring to a boil and add pasta, cooking for 10 minutes.
While the pasta cooks open chicken, add to a colander, give a light rinse and drain well.
In a large mixing bowl beat one egg, add milk, heavy cream, cream of chicken & mushroom, mayonnaise, salt, pepper, thyme, and onion powder and mix together. Mixture will be like a thick creamy liquid.
Crush sleeve of crackers and reserve for topping.
Once the pasta is done, pour into a colander and drain. Add to wet mixture and combine. Add the chicken and combine. Spray a casserole dish. Add layers of the casserole mixture and sprinkle with cheese between layers.
Bake for 20 minutes.
Add the crushed cracker topping and bake for an additional 20 minutes. Casserole will be hot and bubbly.
Remove from the oven and allow to stand 5 minutes before serving.