Arrange rack in center of oven. Preheat to 400ºF.

Whisk together flours, baking soda and salt in a large bowl. Add the honey and buttermilk and stir using a wooden spoon until just combined.

Turn out dough onto a lightly floured surface and knead briefly, about 10 turns, until it forms a relatively smooth ball. Place on a lightly floured baking sheet and shape into a round, flattening it slightly. Using a sharp knife or a lame, cut a deep X into the top of the loaf, taking care not to slice all the way through.

In a small bowl, whisk together the water and egg white. Brush the top and sides of the dough with the egg white mixture. Sprinkle nuts and sunflower seeds on top.

Bake for 30 minutes, then move tray to upper middle rack of oven and bake for 15 more minutes until the crust becomes a deep golden color and internal temperature registers 185ºF on an instant read thermometer. It should sound hollow when tapped with your knuckle. Transfer to a wire rack, and let cool for at least an hour before slicing.

*Make your own oat flour by grinding a little more than 2 cups of old fashioned rolled oats in a food processor until consistency is very fine. Then measure 2 cups oat flour for the recipe.