Preheat oven to 350 degrees F. Combine cream of chicken soup, sour cream, milk, Hidden Valley Ranch seasoning packet, diced onion, and diced jalapeno (optional). Mix to combine.
Melt ½ cup butter and pour it into a 9x13 pan. Add half a package of frozen hash browns to the pan, spreading evenly.
Pour half of the wet mixture over hash browns and use a spatula to spread evenly. Sprinkle 2 cups of shredded cheese evenly over the top of this layer.
Add remaining hash browns. Add remaining half of the wet mixture, using a spatula to spread evenly. Sprinkle the remaining 2 cups of cheese over the top of that layer.
Crush up the package of croutons and sprinkle them evenly over the top of the cheese.
Bake for 45 minutes, uncovered. Remove from oven and let sit for 5 minutes before serving.