Preheat Belgian Waffle iron. In a large mixing bowl, whisk together the buttermilk, eggs, oil and sweet potato. Sift together the unbleached flour, cornmeal, baking soda, baking powder, salt, nutmeg and cinnamon. Gently fold dry ingredients into wet. Stir until no flour is visible.Fold in 1/2 cup pecans. Spray heated waffle iron generously with non stick cooking spray. To make 1 waffle, pour 3/4 cup batter into heated waffle iron, and cook according to manufacturer's directions. When steam stops being released, about 3-4 minutes, remove waffle and place on wire rack.Repeat process with remaining batter to make 4 waffles.
To make Praline Sauce: In a medium saucepan, combine 1 cup light, brown sugar, 1/2 cup water and 1/2 cup butter (1 stick). Bring to boil; boil 2 minutes. Beat 2 eggs in a small bowl. Gradually blend small amount of hot syrup into beaten eggs. Return egg mixture to saucepan; cook over low heat 1 minute, stirring constantly. Remove from heat; stir in 1/2 cup chopped, toasted pecans and 1 tsp. vanilla.
To assemble: Serve hot waffles with warm Praline Sauce and a dollop of sweetened whipped cream. Garnish with toasted pecans and orange slices, if desired.