Grease a 9x5-inch loaf pan. Set aside.
Mix together flours, baking powder, baking soda, and salt in a large bowl. Set aside.
In a medium saucepan, combine remaining ingredients and place over medium-high heat. Bring to a boil, reduce heat, and simmer 5 minutes. Let cool completely.
Preheat oven to 350°F.
Combine flour mixture with the mixture from the saucepan, stirring until just combined. Scrape into prepared pan.
Bake 45 minutes, or until a skewer inserted into the center comes out clean.
Let cool in pan for 15 minutes, then remove from pan to cool completely.
Serve dusted with powdered sugar.