Peel and chop the sweet potato into chunks. Boil for 15–20 minutes or until fork-tender. Drain and mash until smooth (an immersion blender works well for this).
In a large bowl, whisk together the mashed sweet potato, egg, PBfit, honey, melted butter, and vanilla extract until smooth.
Sift in the flour, cocoa powder, and baking powder. Add a pinch of salt. Stir until just combined and smooth.
Fold in ½ cup of dark chocolate chips.
Pour the batter into a greased or parchment-lined 9x9-inch baking pan. Sprinkle extra chocolate chips on top.
Bake at 350°F for 20–25 minutes, or until a toothpick inserted in the center comes out mostly clean.
Let cool before slicing. Enjoy!