I preheated Slow Cooker for about 15 mins
Tea Towel under lid.
My slow cooker seems to cook quick, so keep an eye on them, I lifted lid to just peek and check how they were rising a few times, Careful not to let too much steam out though.
Whisk together flour, sugar, baking soda and baking powder in a large mixing bowl.
Add butter, Nutella, egg whites, vanilla, sour cream and milk and mix on medium speed until smooth.
Fill cupcake liners a little more than half way.
Bake 50 mins to an hours pending on your slow cooker with a tea towel under the lid, The cupcakes are light brown in colour.
While cupcakes cool, make icing.
Mix butter together for 1 minute on medium,
Add 2 cups of Icing sugar and mix until smooth.
Add Nutella and 1 tbsp water and 1tbs cream, mix until smooth.
Add icing sugar and 1 tbsp water and mix until smooth.
Ice cupcakes.
Please note, The butter may make the cupcake batter slightly lumpy, You can leave for a few mins and then mix again for another 30 seconds.