Preheat the waffle maker and grease with cooking spray.
In large bowl, whisk together buttermilk and eggs. Add in the mashed potatoes, spring onion, basil and cheese until well combined.
In a small bowl, mix together flour, baking powder and baking soda.
Gently fold the flour mixture into the potato mixture, season with salt and pepper and mix until well combined.
Pour about 1/2 cup of the waffle batter (depending on the size of your waffle maker) into your waffle maker and spread into an even layer.
Close the lid and bake the waffle until cooked through, crispy and golden brown, about 7-8 mins.
Transfer the waffle to a serving plate then repeat the process with remaining batter.
Serve your sweet potato waffles topped with sour cream and chopped chives or your favorite toppings.
I've used sweet potatoes steamed the day before, but you can also use any left-over mashed sweet potatoes you have in the fridge. If you opt for regular potatoes, the best ones to use are starchy Russets or Yukon Golds potatoes.