Preheat your oven to 400 degrees F.
Spray a 9x13 inch pan with nonstick spray, or grease with butter.
Dump the bag of frozen hashbrowns into the pan. (There is no need to thaw first.)
Melt a stick of butter in a small bowl, and pour evenly over the potatoes. Sprinkle the potatoes with salt and pepper. Use a spoon to gently toss it all together, then spread it out so that it's even.
Bake at 400 degrees for 25-30 minutes, until the potatoes are tender and lightly browned on top. You can even nab a forkful to make sure they are done if you like.
Remove the casserole and reduce the oven temperature to 350.
Layer the Monterey Jack and Cheddar cheese over the top of the potatoes. Add the ham. You can either leave it layered or use a spoon to gently toss the cheese and potatoes and ham together. Either way is fine. (I like to toss for a more even distribution.)
In a large bowl or stand mixer, whisk together 8 eggs, evaporated milk OR cream, seasoned salt, kosher salt, pepper, dry mustard, and onion powder. Beat well.
Pour the egg mixture over the top of the casserole, making sure everything gets wet.
Bake at 350 degrees for about 40 minutes. It is done when bubbly, when the edges start to brown and the center doesn't wiggle when you shake the pan.
If the center of the casserole looks very wobbly but the top is starting to brown too much, cover with foil for the last few minutes of baking.