In a large bowl, combine the water, honey and yeast and let stand for 5-10 minutes until foamy.

In a small saucepan over medium heat, warm the buttermilk. Stir the buttermilk into the yeast mixture followed by 2 cups bread flour, oats, whole-wheat flour, oil and salt. Stir in the remaining flour creating a shaggy dough. (You may not need to use all the flour.) Cover the dough and let it rest for 15 minutes.

On a lightly floured work surface, knead the dough until smooth and elastic, about 10 minutes. Knead in the walnuts. Form the dough into a ball and place in an oiled bowl. Cover and let the dough rise until doubled in size, about 50 minutes.

Punch down the dough. Turn onto a lightly floured work surface and knead a few times before dividing into 3 equal pieces. Roll each into a rope about 16 inches long. Braid the dough and tuck under the ends. Place on a prepared sheet pan and cover. Let rise until almost doubled in size, about 45 minutes.

Preheat the oven to 375 degrees F. Line a sheet pan with parchment.

Whisk together the egg and milk. Brush the loaf with the egg wash and top with oats. Bake the loaf for 50 minutes until it is golden brown and a tester inserted in the center comes out clean. Cool on a wire rack.

Wrap loaf before storing at room temperature.