Preheat the oven to 190C/375F/Gas 5.
Grease a 20cm/8in square cake tin with butter and dust with flour.
Blend the butter and sugar together in a freestanding mixer with a whisk attachment or using a hand-held whisk.
Place the dates and 300ml/10fl oz water in a saucepan and bring to the boil.
Gradually add the golden syrup, treacle, vanilla and eggs to the butter mixture and mix thoroughly. Turn the mixer down to a slow speed and add the flour. Once all the ingredients are combined, turn off the mixer.
Purée the water and date mixture and add the bicarbonate of soda. Quickly stir this into the batter while it is still hot.
Once the mixture is combined, pour it into the buttered and floured cake tin and bake for 40–45 minutes, or until the top is firm to the touch. Leave the pudding to cool in the tin.
Meanwhile, put all the sauce ingredients, except for the cream, into a saucepan. Heat gently until the sugar is dissolved. Add the cream and bring to the boil. Stir the boiling sauce continuously until it reaches the desired consistency.
To serve, cut the pudding into squares and serve with the toffee sauce.