the butter in the microwave or on the stovetop until just liquid. Sprinkle the dry onion soup mix into the melted butter and stir well until the onion flakes and seasonings are evenly moistened and form a thick, fragrant mixture.
Pour the butter and onion soup mixture evenly over the potatoes in the slow cooker. Use a large spoon or your hands to toss the potatoes gently right in the crock, making sure every piece is coated with that buttery, dark onion mixture.
