Makes 6 to 8 servings
1. Microwave butter in a microwave-safe bowl at HIGH 30 seconds to 1 minute or until melted; stir in vanilla and salt.
2. Stir together granulated sugar and brown sugar in a medium bowl.
3. Layer potatoes and sugar mixture in a lightly greased 6-qt. slow cooker, beginning with potatoes and ending with sugar mixture. Pour butter mixture over top. Cover and cook on LOW 4 hours or until potatoes are tender.
4. Transfer potatoes to a serving dish using a slotted spoon, reserving liquid in slow cooker. Keep potatoes warm.
5. Remove 1/3 cup liquid from slow cooker; whisk cornstarch into 1/3 cup liquid until smooth. Carefully pour remaining liquid from slow cooker into a medium saucepan. Whisk in cornstarch mixture. Bring to a boil over medium heat; cook 1 to 2 minutes or until thickened. Pour over potatoes. Serve immediately.