Preheat oven to 375F; butter and flour two 9x5-inch loaf pans.
In a large bowl, whisk together oil, honey (if you measure out the oil first, and then put honey in the oiled measuring cup, the honey will come out easier) eggs and sweet potato puree until creamy.
In a small bowl, combine both flours, sugar, baking soda, salt and spices.
In a measuring cup, combine buttermilk, balsamic vinegar and vanilla extract.
Fold dry ingredients into sweet potato mixture, alternating with buttermilk; mix until just combined; if using pecans and/or raisins, toss them with 1 tblsp flour and fold them into the batter quickly; scrape batter into prepared loaf pans and bake for about 60 minutes, or until breads test done when toothpick is inserted into centre and comes out clean; if bread appears to be browning too quickly, tent loosely with some foil and continue baking (I did this about 1/2 an hour into baking).
Cool in pan for 10 minutes before removing.
Note: Like most quick breads (and cakes), this slices up best a day after baking- I couldn't wait!