Adapted from Annie's Eats.
1½ cups rolled oats, divided
1 cup boiling water
¼ cup room temperature water
2 tbsp. + 1 tsp. agave nectar (or honey), divided
2 tsp. instant yeast
1½ cups buttermilk, at room temperature*
½ cup extra virgin olive oil
2½ cups whole wheat flour
2½ cups all-purpose flour
2 tsp. salt
*a substitute for buttermilk can be made by adding 1 Tbsp vinegar or lemon juice for every 1 Cup of milk. Let the mixture sit (and curdle) for at least 5 minutes.
Set aside ¼ cup of the rolled oats. Place the remaining oats in a medium bowl. Cover with the boiling water, mix well, and let sit uncovered for 10 minutes, stirring occasionally.
In the bowl of a stand mixer fitted with the paddle attachment, combine the soaked oats, room temperature water, 2 tablespoons of agave, yeast, buttermilk, olive oil, 2 cups of each flour, and salt. Mix briefly on low speed until ingredients are combined. Mix in the remaining ½ cup of each flour.
Switch to the dough hook and knead on low speed for about 10 minutes. The dough will be wet, cling to the hook, and have a satiny finish. (My mixer started getting a bit overheated, so when it was nearing completion of the kneading process I removed the dough onto a lightly floured surface, floured my hands and kneaded manually until no longer overly sticky.)
Place the dough in a lightly oiled bowl, turning once to coat. Cover the bowl with plastic wrap, and let the dough rise in a warm place for 1 hour or until doubled in bulk.
Turn the dough out onto a lightly floured surface, flattening it with your hands to release the excess air bubbles. (I found that the dough could be divided in half to form two regular sized loaves. They may be a bit smaller than the original, but they're just wonderful!) Form the dough into a 12 x 6-inch rectangle and position it so the long side is facing you. Fold the two shorter ends onto the top so that they meet in the middle. Starting with the closest end, roll the dough away from you tightly into a log. Pinch the seam closed. Transfer the loaf to an oiled loaf pan, pressing it so that it reaches all the corners. Mix the remaining agave nectar with ½ a teaspoon of very hot water. Brush over the top of the loaf, and sprinkle with the reserved oats. Let rise for about 30 minutes, just until the loaf rises over the top of the pan.
Preheat the oven to 375˚ F. Bake the loaf for 1 hour (or, if baking two loaves, bake for 25-30 minutes.) Bread is done when it sounds hollow when tapped with your fingertips. Remove from the oven, transfer to a wire rack and allow to cool completely before slicing.