Chop the dates and sprinkle with bicarbonate of soda. Pour over the boiling water and set aside.
Beat the butter, caster sugar, and dark brown sugar in a large bowl until fluffy.
Add the vanilla, salt, eggs, and flour, then gently beat for 2 minutes until smooth.
Add the date mixture and beat again for 1 minute. Spoon into a tin and bake at 180°C/160°C fan/gas 4 for 35-40 minutes.
To make the toffee sauce: melt the butter, dark brown sugar, and treacle in a pan until bubbling. Remove from heat and stir in the cream.
Once the traybake has cooled, pour over the toffee sauce and enjoy!
