Inspired by Mary Berry's sticky toffee pudding: a treacle sponge baked soft, drowned in a butterscotch sauce made from the same ingredients twice over.
Heat the oven to 180°C (160°C fan) and butter a wide, shallow 1.7-litre ovenproof dish.
Put the butter, sugar, eggs, flour, baking powder, bicarbonate of soda and treacle into a bowl and beat with an electric whisk for about 30 seconds, until combined. Pour in the milk gradually, whisking until smooth.
Pour into the prepared dish and bake for 35 to 40 minutes, until well risen and springy in the centre.
For the sauce, put all the ingredients into a saucepan and stir over low heat until the sugar has dissolved and the butter has melted. Bring to the boil and stir for a minute.
Pour half the sauce over the warm pudding in the dish, and serve with the rest alongside, plus cream or ice cream.
Save the rest of the sauce for pouring over each portion at the table sticky toffee pudding only gets better with too much sauce, not less.