Preheat the oven to 400°F / 205°C with a rack in the middle of the oven. Butter and line a 9x5x3 inch loaf pan (or one with ~8 cup capacity) with parchment paper and set aside. Alternately, you can bake this bread without a pan, shaped like this, on a lightly floured baking sheet.
To make the oat flour, use a food processor to pulse the rolled oats a few times. Then process into a fine powder - another minute or two. If you are buying oat flour, not making your own, measure out 7 oz / scant 2 cups.
Sift the flours, baking soda, and salt into a large bowl. Make a well in the flour and pour in the buttermilk. Stir just until everything comes together into a dough. Turn out onto a lightly floured countertop and knead for 30 seconds or so, just long enough for the dough to come together into a cohesive, slightly flattened ball without many cracks or fissures. If your dough is on the dry side, add more buttermilk a small splash at a time. Now ease the dough evenly into the prepared baking pan - see photo if you need a bit of guidance.
Brush all over the top and sides with buttermilk and sprinkle generously with mixed seeds or flour, 2 tablespoons or so. Slice a few deep slashes across the top of the dough. Bake for about 30 minutes, then quickly (without letting all the hot air out of the oven), move the rack and the bread up a level, so the top of the bread gets nice and toasted. Bake for another 20 minutes, or until a hard crust forms and the bread is baked through. It will feel very solid and sound hollow when you knock on it. Carefully lift it out of the pan, in a timely fashion, and allow to cool on a wire rack. Enjoy with a good slathering of salted butter.
Makes one loaf.
Prep time: 10 min - Cook time: 50 min
