How to Make It
Preheat oven to 350°.
Weigh or lightly spoon potato starch and flours into dry measuring cups; level with a knife. Combine potato starch, flours, granulated sugar, and next 4 ingredients (through salt) in a medium bowl; stir with a whisk. Make a well in center of mixture. Combine orange juice, oil, and eggs; stir with a whisk. Add to flour mixture, stirring just until moist. Fold in cranberries and walnuts.
Pour batter into a 9 x 5-inch loaf pan coated with cooking spray, and sprinkle with turbinado sugar. Bake at 350° for 50 minutes or until a wooden pick inserted in center comes out clean. Cool 15 minutes in pan on a wire rack; remove from pan. Cool completely on wire rack.
If you're planning to freeze this loaf, leave off the turbinado sugar.