Rinse the dried white field corn under cool water. In a large nonreactive pot, bring 8 cups water to a boil and stir in the calcium hydroxide until dissolved. Add the corn, return to a simmer, and cook over medium-low heat until the kernels’ skins rub off easily when pinched, 25–35 minutes. Remove from heat, cover, and let soak 8–12 hours.
Drain the nixtamalized corn and rinse under running water, rubbing kernels between your hands to remove loosened hulls until the water runs mostly clear. Drain well.
Grind the corn: Working in batches in a food processor or high‑power blender, process the corn with 1 cup fresh water until a smooth, slightly sticky dough (masa) forms, 5–10 minutes total. Scrape down as needed; add just enough water for the blades to move.
Roast the cacao beans in a dry skillet over medium‑low heat, stirring constantly, until fragrant, a shade darker, and the husks begin to loosen and sound papery, 10–15 minutes. Cool 5 minutes, then rub the beans between your hands or in a clean towel to remove husks; discard the husks.
Grind the roasted cacao in a food processor, spice grinder, or mortar and pestle until it forms a moist paste that clumps together, 2–4 minutes.
Combine the cacao paste with the corn masa in a bowl and knead until uniform and chocolate‑brown, 3–5 minutes. Divide into 6 equal balls, place on a plate, and cover. Ferment at room temperature 12–24 hours (70–77°F/21–25°C) until a light, pleasantly sour aroma develops; this fermentation is characteristic of pozol.
Break the fermented masa‑cacao balls into pieces in a large pitcher. Add 6 cups cold water gradually while whisking (or working with a clean hand) until smooth and pourable with a fine, earthy sediment that settles slowly, 2–3 minutes. Sweeten to taste with the sugar.
Pour into cups over ice and serve immediately. Stir between sips as the masa naturally settles.