In a small bowl, mix warm water, yeast, and 1 tsp molasses. Let sit for 5–10 minutes until frothy.
In a large bowl, combine remaining molasses, apple cider vinegar, and yeast mixture.
In another bowl, whisk together bread flour, rye flour, cocoa powder, salt, and caraway seeds (if using).
Gradually add dry ingredients to wet ingredients, mixing until a sticky dough forms.
Knead by hand (10 minutes) or with a stand mixer (5–7 minutes) until smooth and elastic.
Place dough in a greased bowl, cover with a towel, and let rise in a warm place for 1–2 hours, or until doubled.
Punch down dough, shape into a loaf, and place in a greased loaf pan dusted with cornmeal.
Cover and let rise for 45–60 minutes.
Preheat oven to 375°F (190°C).
Bake for 40–45 minutes until the loaf sounds hollow when tapped.
Cool on a wire rack before slicing.
