For the stovetop method, place a steamer rack inside a tall stockpot and add enough water to reach one-third of the height of the coffee can. Set the pot over medium heat while preparing the batter.

For the oven method, preheat the oven to 325°F (163°C). Bring a large pot of water to a boil.

Thoroughly grease a clean coffee can or a small loaf pan with butter, ensuring all inner surfaces are coated.

In a large bowl, whisk together the all-purpose flour, rye flour, finely ground cornmeal, baking powder, baking soda, kosher salt, and allspice. Add the raisins, if using, and mix to distribute evenly.

In a separate bowl, whisk together the buttermilk and vanilla extract, if using. Add the molasses and whisk until the mixture is smooth and fully incorporated.

Pour the wet mixture into the dry mixture and stir until a thick, cohesive batter forms. Do not overmix.

Transfer the batter into the prepared coffee can or loaf pan, ensuring the batter does not exceed two-thirds of the container’s height. Cover the top securely with foil to seal in moisture.

For the stovetop method, place the container onto the steamer rack. Add additional water if necessary so it remains one-third up the sides. Cover the pot and reduce the heat to the lowest setting that still maintains a gentle simmer. Steam for 2 hours and 15 minutes, checking the water level periodically to prevent boiling dry.

For the oven method, place the filled container inside a high-sided roasting pan. Pour boiling water into the roasting pan until the water reaches one-third up the sides of the container. Carefully transfer the pan to the oven and steam for 2 hours and 15 minutes.

Insert a toothpick into the center of the bread. If it emerges clean, the bread is done. If not, re-cover the container and continue steaming for an additional 30–45 minutes.

Remove the container from the heat. Allow the bread to cool for 10 minutes before transferring it to a cooling rack. Let it cool for at least 1 hour before unmolding.