tender all the way through.
Lightly grease the inside of your slow cooker with a bit of butter or nonstick spray if you like, just to make cleanup easier. Place all of the quartered red potatoes into the slow cooker crock in an even layer.
In a small bowl or measuring cup, melt 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.