Scrub the whole fingerling potatoes well under cool water and pat them dry. If any potatoes are much larger than the others, cut them in half so they cook evenly, but leave most of them whole.

Place the potatoes in the slow cooker. Sprinkle the ranch seasoning evenly over the top, then add the butter pieces over the potatoes.

Cover and cook on low for 4 to 5 hours or on high for 2 to 3 hours, until the potatoes are fork tender. About halfway through cooking, gently stir or shake the slow cooker insert if needed so the potatoes get coated in the melting butter.

Once tender, toss the potatoes gently in the buttery glaze and transfer them to a serving board or bowl. Spoon any extra butter from the slow cooker over the top before serving warm.