Step 1

Heat the oven to 185C (165C fan)/360F/gas 4½. Pour the syrup into a 18cm x 28cm x 5cm baking dish, or similar, add 50ml boiling water, mix well and set aside.

Step 2

In a stand mixer, food processor or large bowl with a wooden spoon, beat the butter, sugar, lemon zest and a pinch of salt until pale and creamy.

Step 3

Add the eggs one at a time, mixing well after each addition; if the mixture starts to curdle, add a spoonful of the flour.

Step 4

Mix in the flour and baking powder to make a smooth batter, then stir in the lemon juice.

Step 5

Spread the batter evenly over the treacle mixture, then cover the dish with foil, sealing the edges to trap the steam.

Step 6

Bake for 35 minutes, until a skewer inserted into the centre comes out clean.

Step 7

Remove the foil and serve hot, ideally with custard.