Place the raw baby potatoes in an even layer in the bottom of the slow cooker. They should sit snugly but still in a single layer or only slightly mounded.
Scatter the remaining butter pieces evenly over the potatoes. Sprinkle the kosher salt over the top so it seasons the potatoes and the cooking liquid.
Slowly pour the can of evaporated milk over the raw potatoes in the slow cooker, making sure the milk drizzles down through the gaps between the potatoes. The potatoes will not be fully submerged; that’s fine, as they will release moisture while cooking.
Cover the slow cooker with the lid and cook on LOW for 4 1/2 to 5 1/2 hours, or on HIGH for 2 1/2 to 3 hours, until the potatoes are very tender when pierced with a fork. Avoid lifting the lid during the first couple of hours so the heat and steam stay consistent.
Once the potatoes are tender, gently stir from the bottom with a broad spoon, turning the potatoes over so they are coated in the thickened evaporated milk and butter sauce. Taste the sauce and add a pinch more salt if needed.
Let the potatoes sit on the WARM setting for 10 to 15 minutes before serving; this resting time allows the sauce to thicken slightly as the starch from the potatoes continues to mingle with the milk.
Serve the potatoes hot straight from the slow cooker, spooning plenty of the creamy sauce over each portion.
To keep the spirit of the original 4-ingredient, pantry-staple recipe, treat these ideas as optional tweaks you can add once you’ve tried the base version. For a peppery kick, add 1/2 teaspoon of freshly ground black pepper along with the salt. If you’d like a slightly richer sauce, stir in 1/4 cup grated Parmesan or a small handful of shredded cheddar during the last 10 minutes of cooking, just long enough to melt. Fresh herbs aren’t traditional but are lovely if you have them on hand—sprinkle chopped parsley or chives over the finished dish for color and brightness. You can also add sliced onions or a few smashed garlic cloves under the potatoes before pouring in the evaporated milk; they’ll soften into the sauce and add gentle sweetness and aroma. For a complete one-pot meal, tuck a few browned sausage links or diced cooked ham around the potatoes at the beginning of cooking so the meat flavors the sauce as everything simmers together.
