Open and drain sweet potatoes, add to food processor with milk, brown sugar, butter and vanilla. Pulse until well combined and smooth.
In a large bowl, mix together flour, baking powder and salt. When well combined, stir in sweet potato mixture.
Add egg whites to stand up mixer and whisk on high until stiff peaks form. Fold egg whites into the batter, 2 cups at a time. Once it’s well incorporated, scoop about 1 cup of batter onto a hot greased waffle iron and cook for about 5 minutes or until slightly golden and crispy.
Warm up maple syrup in a pot on low heat. Once warmed, stir in cinnamon.