Rinse, dry, and slice potatoes into 3/4" slices. Leave the skins on so they stay together better. Add into slow cooker, spread out into an even layer.
In a small bowl, combine olive oil, melted butter, half and half and onion soup mix and whisk until combined well. Pour on top of potatoes and toss to coat.
Cover and cook on low for 3-4 hours on low or high 2 to 2-1/2 hours, stirring 1 hour after start time. If you want to melt shredded cheese on top add the last 30 minutes. Enjoy when they are fork tender.