Whisk milk, eggs, maple syrup, vanilla and cinnamon together in a large bowl. Add the cubed bread and allow to soak for 10 minutes.
Grease the slow cooker well with the butter. Add the cranberries and walnuts to the bread mixture and transfer everything to the slow cooker. Cook on low for 4 hours.
To Make The Caramel Sauce:
Add the condensed milk, brown sugar and butter to a medium saucepan over medium heat. Stir continuously until bubbly and thickened. Add a pich of sea salt if you like. Serve warm with the hot bread pudding.
If you don't like walnuts and cranberries, feel free to leave them out. You can also use raisins instead of the cranberries, if you prefer.