vanilla ice cream or double cream, to serve (optional)
Butter a 1.2-liter pudding bowl and dust it with flour. Place an upturned heatproof saucer inside a big saucepan (deep enough to contain the bowl) on the stove. Fold a 4cm pleat in the middle of a large sheet of foil that has been greased.
Pour 200ml boiling water over 200g dates and bicarbonate of soda in a heatproof bowl. Allow it soak for 15 minutes before stirring and mashing with a fork.
Meanwhile, in a mixing dish, cream 75g butter, 2 tbsp treacle, the syrup, and 150g sugar for 5 minutes with an electric mixer. Add the beaten egg in small increments, beating well after each addition. Combine the flour and ground ginger in a mixing bowl. Sift half of the flour into the mixing bowl and whisk in carefully, then add the remainder. Add the date mixture and stir to combine.
Pour the mixture into the pudding bowl. Cover with foil so that the pleat is in the middle. Make a string handle across the top of the pudding bowl and secure it with string around the side. Pour boiling water halfway up the sides of the pudding bowl on top of the saucer in the pan. Bring to a boil, then reduce to a low heat and keep covered. Steam for 2 hours, or until a skewer inserted in the center comes out clean, topping up the water as needed.
In a saucepan, combine 1 tablespoon treacle, 150 grams butter, 200 grams sugar, the stem ginger, and 120 grams dates for the sauce. Heat until the sugar has melted, then add the cream and sherry and mix to combine. To thicken, boil for 5 minutes.
Invert the pudding onto a platter that has been warmed. Using a cocktail stick, prick all over and generously brush with sauce. Serve in slices with additional sauce spooned on top and ice cream or cream on the side, if desired.