1. Pour warm water into the bowl of a stand mixer. Sprinkle with yeast and stir with the paddle attachment.
2. Let sit for about 5 minutes, until the yeast 'blooms'.
3. Gently heat buttermilk, butter and honey in a small pot over low heat. Stir just until butter is melted. Make sure the liquid does not get too hot or it will kill the yeast. Wrist warm is good.
4. Add buttermilk mixture, oats and whole wheat flour to yeast mixture. Beat on low speed for about a minute.
5. Let this sponge sit for 30 minutes so the whole grains will absorb the liquid.
6. Replace the paddle attachment with the dough hook.
7. Add salt.
8. Add sifted spelt flour cup at a time, beating on low speed until all the flour is incorporated and a ball of dough forms. Knead the dough on low speed for 6 minutes. Dough will feel smooth and will pull away from the sides of the bowl.
9. Transfer dough to a large, oiled bowl, cover with a tea towel and let rise in a warm place until doubled in size, about 1 hour.
10. Oil two loaf pans.
11. Combine cinnamon and sugar in a small bowl. Turn the dough onto a floured surface and cut in half.
12. Roll each half into a rough 10-inch square.
13. Brush all over with beaten egg, then sprinkle both pieces of dough with cinnamon sugar.
14. Roll each piece of dough up like a jelly roll, tuck in the sides and place in a loaf pan.
15. Let loaves rise, covered with a clean tea towel, just until doubled in size, about 45 minutes. Meanwhile, preheat oven to 375F (190C).
16. Bake loaves for about 40 minutes, until dark golden and loaves sound hollow when thumped. Turn out onto racks to cool slightly, then slice and serve warm.