Mix together challah, dried fruit, and chocolate chips in a large bowl. Transfer to slow cooker. Whisk together half-and-half, yolks, Nutella, sugar, and vanilla in the bowl until well combined. Pour over bread in slow cooker and press gently so the mixture seeps in. Cover and cook on low until set, 2 1/2 to 3 hours. Let cool 15 minutes before serving.