Preheat the oven to 350ºF and line a 9-inch square pan with parchment paper.
In a large bowl, combine the mashed sweet potato, almond butter, cacao powder, coconut sugar, flour, baking powder, vanilla extract, and salt. Stir well, until a relatively smooth batter is formed. (You can do this in a food processor, if you prefer.)
Fold in the chocolate chips, if using. Transfer the batter to the prepared pan and use a spatula to smooth the top. Bake at 350ºF until the edges look dry and the center of the brownies have puffed up, about 35 to 40 minutes.
Let the brownies cool completely before slicing, or they will be too soft. Cut them into 16 small squares, and store the leftovers in an airtight container in the fridge. I think they taste even better when you serve them cold from the fridge the next day! Leftovers can be stored in the fridge for up to a week, or in the freezer for up to 3 months.