Scrub sweet potato; wrap in aluminum foil. Bake at 350° for 45 minutes to 1 hour. Cool completely. Scoop out pulp, and mash to equal 3/4 cup. Set aside.
Melt 1 tablespoon butter in a small skillet over medium heat. Add pecans; cook, stirring constantly, 6 minutes or until toasted. Remove from heat; cool completely.
Combine flour, baking powder, and salt in a large bowl. Cut 1/2 cup butter into flour mixture with a pastry blender until crumbly; stir in pecans. Combine 3/4 cup mashed sweet potato, sour cream, brown sugar, and maple syrup; add to flour mixture, stirring just until dry ingredients are moistened.
Turn dough out onto a heavily floured surface; knead 6 to 8 times, and pat into a 7" square (3/4" thick). Cut dough into 9 squares; place squares 2" apart on a lightly greased baking sheet.
Bake at 425° for 15 minutes or until lightly browned. Brush with melted butter. Serve warm.
Fix it Faster: Pierce sweet potato skin with a knife, and microwave potato on HIGH 3 to 5 minutes; let stand 5 minutes after cooking. Bake or microwave sweet potato up to a day ahead, and mash. Chill overnight.