Preheat the oven to 350°F and lightly grease your dish. Put the chopped dates, boiling water, and baking soda into a bowl, give a stir, and then leave for 10 minutes.
Cream the butter and molasses until well mixed, then add the sugar and mix again, beating out any lumps. Beat in an egg and keep beating – scraping down as necessary – until completely incorporated, then repeat with the other egg. Beating more gently, add the flour and baking powder until you have a smooth, thick batter.
Using a fork, stir the soaked dates, squishing them a bit, then pour the dates and their liquid into the batter and eat gently to mix in.
Pour and scrape into your prepared dish and bake in the oven for 30-35 minutes, or until a cake tester comes out clean.
While the sponge is in the oven, you can make the sauce. Melt the butter, sugar, and molasses over a very low heat in a heavy-based saucepan. Once the butter’s melted, stir gently until everything else is melted too. Now stir in the cream, then turn up the heat and when it’s bubbling and hot, take it off the heat.
As soon as it’s out of the oven, prick the cooked sponge all over with a toothpick and pour about a quarter of the warm sauce over, easing it to the edges with a spatula so that the sponge is entirely topped with a thick sticky glaze. Put a lid on the remaining sauce in the pan to keep it warm.
Leave for 20-30 minutes, or up to 1 hour, then take to the table, with the rest of the sauce in a pitcher, and cream to serve.