In a stand mixer bowl, add warm water. Sprinkle yeast over top, then add sugar. Whisk briefly and let sit 5 to 10 minutes until foamy. If it does not become foamy you'll need to start again with new yeast (either yeast is too old or water was too warm).
Using the paddle attachment, stir in honey, molasses, and whole wheat flour until just combined. Scrape down sides then let sit 10 minutes.
Add 2 cups bread flour, cocoa powder, salt, and melted (but NOT hot) butter (scrape in every last bit). Mix on low until dough comes together, all gathering around the hook, about 2 to 3 minutes. If it is not gathering (too sticky), add flour 1 tablespoon at a time, up to about 1/4 cup extra.
Put at speed 2 and knead 8-12 minutes, until dough looks smooth and elastic. When you press your finger into the dough it should bounce back.
Lightly grease a bowl with olive oil. Shape dough into a ball, turn to coat in the oil at the base of the bowl, cover, and let rise in a warm environment until doubled, about 1 hour.
Dump dough out of bowl onto a clean surface and use a scale to see how much it weighs. Divide it into 3 equal pieces. Working one piece at a time, roll and shape it into an even 8-inch baguette. Pinching the edges of the dough neatly underneath. Spread cornmeal on surface and press the bottoms of the baguettes into the cornmeal, then place on a parchment-paper lined sheet pan well spaced apart. Cover with a dish towel and let rise until doubled, about 30-60 mins.
Preheat oven to 350°F. Right before baking, using a pastry brush, brush the tops of the bread lightly with water. Gently sprinkle the oats on top. Bake 25-30 minutes, until golden and the loaf sounds hollow when tapped.
Remove and let cool on pan for 15 minutes. Transfer to a wire rack and cool at least 30 minutes before slicing (bread is still baking with carryover heat!). Slice with a sharp bread knife and serve warm with softened butter.
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Notes
Storage: Store cooled bread in an airtight bag at room temp for up to 3 days, though it’s best the same day. Skip the fridge since it dries out the bread. For longer storage, wrap tightly and freeze up to 3 months. Thaw at room temp and warm in the oven or toast slices.