Scrub and rinse sweet potato. Prick it all over with a fork. Roast in 350°F (180°C) oven for 45 to 50 minutes. Remove and let cool. Peel and mash well.
Grease and flour a loaf pan.
In a medium bowl, combine all-purpose flour, baking powder, baking soda, salt, cinnamon, and cloves. Set aside.
In a large bowl, combine sugar, egg, vegetable oil, buttermilk, and sweet potatoes. Add dry mixture to sweet potato mixture. Stir until well combined. Fold in pecans. Spoon batter into loaf pan.
Bake in a 350°F (180°C) oven for 55 to 60 minutes. Remove and cool on a wire rack for 10 minutes. Remove bread from pan and allow it to cool completely.