Add 2 cups of the shredded cheddar cheese to the soup mixture and stir until the cheese is evenly distributed.
Add the cubed potatoes to the bowl and gently fold until every piece is well coated in the cheesy mixture.
Transfer the potato mixture to the prepared slow cooker, spreading it into an even layer. Dot the top with the butter pieces, if using.
Cover and cook on HIGH for 3 to 4 hours or on LOW for 6 to 7 hours, until the potatoes are tender when pierced with a fork and the edges are bubbly.
Once the potatoes are tender, sprinkle the remaining 1 cup shredded cheddar cheese evenly over the top. Cover again and cook on HIGH for 10 to 15 minutes, just until the cheese is fully melted and gooey.
Switch the slow cooker to the WARM setting for serving. Give the potatoes a gentle stir at the edges to mix in some of the melted top cheese while still leaving a cheesy layer on top. Serve straight from the slow cooker with a large spoon so you get those stretchy, golden cheese pulls.
To keep this a true 4-ingredient base, think of the core as potatoes, cheddar, cream of chicken soup, and sour cream—everything else is optional flavor. For a vegetarian version, swap the cream of chicken soup for cream of mushroom or cream of celery. If you like a little color and texture, stir in 1/2 cup finely chopped green onions or chives before cooking, or scatter them over the top just before serving. For extra smokiness, add 1/2 teaspoon smoked paprika to the sauce or fold in 1 to 1 1/2 cups cooked, crumbled bacon or diced ham before transferring to the slow cooker. You can also play with the cheese: use half cheddar and half Monterey Jack or Colby Jack for a milder, extra-melty finish. If your brunch timing is tricky, cook the potatoes on LOW, then keep them on WARM for up to 1 1/2 hours, stirring occasionally around the edges to prevent scorching. If the mixture ever looks too thick, you can gently fold in a splash or two of milk to loosen it back up.
