In my neck of the woods, that's a shortcut recipe for "funeral potatoes", a variation on cheesy au gratin potatoes with less work but a ton of fat and sodium. Having made such things decades ago, I'd skip the cream cheese idea totally. Non-fat cream cheese will behave terribly in this dish and whole fat would too. I don't see the benefit of trying to substitute the canned soup compared to the rest of the processed fats and sodium in the potatoes.
I'd bail on the whole pre-processed aspects personally but that may not be what you want to do.
I'd do something along these lines:
3 cups milk
2 pounds russet poatoes peeled and cubed 1/4-1/2 inch dice
1/2 onion, diced, approximately 1/2 cup
1 clove of garlic, minced 2 if you're fond of garlic like me
3 tablespoons butter
1/2 teaspoon dried thyme (poultry seasoning would work well to and I'd probably increase the amount a bit if I used that)
salt and pepper to taste
1/4 cup flour
2 cups shredded cheddar.
In a saucepan on medium heat, combine the milk and potatoes. Simmer for 10 minutes, avoid boiling as the milk will curdle. This parcooks the potatoes. Will probably take about 20 minutes total counting the heat up time but will vary depending on your stove. Timing this and the following step to coincide correctly is nice but has too many variables to be precise in writing. Let your experience guide you or just work each step separately will work out too.
While the potatoes are simmering. Heat a 12" saute pan over medium high heat. Add the butter, when the foaming stops, add the onions. Saute about 2 minutes, then add the garlic and thyme. Saute a few minutes more but stop if the garlic starts to color, Add the flour and stir well to make a roux with the onions and butter. Cook this a minute. Ideally, the pootatoes and milk are done at this point and you could add them to the pan, stirring to combine and thicken the milk. Season with salt and pepper to taste. This will need to come to a boil briefly to thicken properly.
Now you combine it in the casserole with the cheese as in the original recipe. Bake until bubbly and the cheese is browned. I personally skip the corn flakes as I'm not that impressed with them, but you could certainly use them.