01 - Set oven to 400°F and line a baking sheet with parchment paper.
02 - Whisk together all-purpose flour, whole wheat flour, sugar, baking soda, and salt in a large bowl.
03 - Stir cranberries and walnuts into the dry mixture, ensuring they are evenly coated with flour.
04 - Whisk buttermilk, melted butter, and egg together in a separate bowl.
05 - Pour wet ingredients into dry ingredients and gently mix with a wooden spoon or hands until a shaggy dough forms; avoid overmixing.
06 - Turn dough onto a lightly floured surface and form into a round loaf approximately 7 inches in diameter.
07 - Place loaf on prepared baking sheet; score a deep X on top with a sharp knife to promote even baking.
08 - Brush the top of the loaf with a small amount of buttermilk.
09 - Bake for 35 to 40 minutes, or until the bread is golden brown and a skewer inserted in the center comes out clean.
10 - Allow the loaf to cool on a wire rack for at least 30 minutes before slicing.