Prep Potatoes: Prepare the potatoes first. Rinse the red potatoes under cool water and scrub off any dirt. Pat them dry with a towel, then cut each potato into quarters so the pieces are all roughly the same size. This helps them cook evenly and get tender all the way through.

Prep Slow Cooker: 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.

Mix Butter & Seasoning: 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.

Coat Potatoes: 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. The potatoes should look glossy with visible onion flakes clinging to the skins.

Cook: Cover the slow cooker with the lid and cook the potatoes on LOW for 4 to 5 hours, or on HIGH for about 2 to 3 hours, until the potatoes are very tender when pierced with a fork. During the last hour of cooking, lift the lid once or twice and gently stir so the butter and onion coating redistributes and the potatoes cook and brown evenly along the edges.

Serve: Once the potatoes are fork-tender and coated in a rich, dark, glossy onion-butter sauce, turn off the slow cooker. Give them one last gentle stir to pick up any flavorful bits from the bottom of the crock. Spoon the potatoes onto a white plate or serving dish, letting the caramelized onion butter drizzle over the top, and serve hot.