In a large mixing bowl, combine the breadcrumbs, flour, raisins, ginger, and cinnamon.

In a separate bowl, whisk together the melted butter, molasses, dark rum, and beaten egg.

Dissolve the baking soda in the tablespoon of hot water, then stir it into the wet molasses mixture.

Pour the wet ingredients into the dry ingredients and stir until well combined into a stiff batter.

Grease a heatproof pudding basin or a small metal mixing bowl generously with butter.

Spoon the batter into the greased bowl. Cover the top tightly with a piece of parchment paper followed by a piece of aluminum foil, securing it around the rim with kitchen twine.

Place the bowl into a large pot and fill the pot with boiling water until it reaches halfway up the sides of the pudding bowl.

Cover the large pot with a lid and simmer gently for 90 minutes. Check occasionally to ensure the water hasn't boiled away, adding more boiling water if necessary.

Carefully remove the pudding bowl from the pot and let it rest for 10 minutes before removing the foil and turning it out onto a plate.

Serve warm, traditionally sliced and topped with a simple butter sauce or whipped cream.