In a large mixing bowl, whisk together dry ingredients. Add wet ingredients and sultanas, if you like, and stir to form a smooth batter.

Butter the mold thickly and add batter (to about one-third of the way). Cover the pan with buttered foil and tie it in place with a string.

Place the mold in a steamer pot over 2 inches of rapidly boiling water (you’ll need to add more water as it cooks). Cover and cook 2-3 hours, until a toothpick inserted into the center emerges clean.

Unmold on a cooling rack and let cool slightly. Serve warm, slathered with butter.