Step 1In a medium saucepan over medium heat, melt the butter. Add the sugar and stir until it is dissolved. Whisk in the water and simmer for 8 to 10 minutes until thickened. This makes about 1 cup sauce.
Step 1Scrub the sweet potatoes and pierce them all over with a fork. Microwave on high until they are easily pierced through with a knife or fork, 6 to 7 minutes. Slit the sweet potatoes lengthwise and set aside until just cool enough to handle, about 5 minutes.
Step 2While the sweet potatoes are cooling, in a large mixing bowl, sift together the whole wheat flour, all-purpose flour, baking powder, salt, nutmeg and cinnamon. Set aside.
Step 3Spoon the flesh of the warm sweet potatoes into a bowl and measure 1 1/4 cups (discard any remainder, or save for another use). Transfer the 1 1/4 cups sweet potatoes into the bowl of a food processor. Add the butter and process until smooth. Add the eggs and brown sugar and continue to process until smooth. Add as much of the buttermilk as will fit and process until smooth.
Step 4Spoon the sweet potato mixture and the remaining buttermilk, along with the vanilla and molasses, into the large bowl with the dry ingredients and stir just until combined. If the batter is too thick, adjust the consistency as desired with a little more buttermilk.
Step 5Heat a skillet or griddle over medium heat. Lightly oil the griddle and drop heaping spoonfuls of batter onto the hot griddle. When the pancakes set and start to bubble, flip and cook until golden. Serve with the brown sugar butter sauce and garnish with toasted pecans.