Preheat oven to 425°F. Wash the sweet potatoes and poke them all over with a fork.
Roast them on a foil-lined sheet pan for an hour, or until fork tender.
Remove the sweet potatoes and let them cool down enough to be handled. Remove the flesh and run it through a food processor to get a sweet potato puree.You'll need 2 cups of puree for the brownies, and 1 cup for the frosting. In a large mixing bowl, stir together the sweet potato puree, melted coconut oil, vanilla extract, eggs, maple syrup, and cocoa powder until combined.
In a separate bowl, mix the flour, baking powder, salt, and chopped pecans.
Pour the dry ingredients into the wet bowl, a little at a time, and mix.
Preheat your oven to 350°F. Take a 9x9 brownie pan and line the bottom with parchment paper.
Pour the brownie mixture into your baking pan and bake for about 25 minutes on the center rack.
Let the pan cool completely, either on the counter or in the refrigerator.