If you can’t find teeny-tiny potatoes, use halved baby potatoes. Place them cut-side-down before smashing. You may have to adjust the roasting time depending on size.
You can use any fat, but the bacon grease is really what makes these potatoes SHINE. While traveling down south, I came across a product called Bacon Up - shelf stable bacon grease. I am now addicted. You can find it online, and it’s worth every penny!