Preheat oven to 350 degrees.
Line 10" round baking pan with parchment on the bottom.
Spray parchment lined pan with cooking spray on bottom & sides. Set aside.
In microwave safe bowl- place sweet potato in with enough water to cover bottom.
Pierce sweet potato several times- microwave approx 10 minutes. Turn over- microwave another 5-10 minutes until soft like a baked potato. Set aside.
Melt chocolate in microwave safe bowl - about 20 seconds. Set aside.
In large bowl whisk together flour, baking powder, salt. Set aside.
In small bowl, remove skin from sweet potato- mash with fork until no more lumps remain.
Use electric mixer, beat butter & brown sugar until fluffy.
Beat in eggs one at a time.
Reduce mixer to low- mix in mashed sweet potato & then melted chocolate.
Add flour & turn on low- pouring in milk as it mixes the flour into mixture.
Spread batter into your prepared pan.
Bake 35-48 minutes- or until toothpick test is clean.
Cool in pan 15 minutes.
Flip onto wire rack to cool completely.
Flip back to right side onto serving plate.
Sprinkle powdered sugar or add icing of choice to taste.