Heat oven to 180°C (160°C fan). Grease and line a 32 x 21 cm deep tray.
Place chopped dates in a bowl, pour over boiling water, treacle and add bicarb and leave to soften.
In another bowl, beat butter, oil, and sugar until pale. Add eggs one at a time, then whisk in sour cream, orange zest and juice, and vanilla.
Fold in the flour, cinnamon, and ginger until just combined. Stir through the softened date mixture (it will look loose, that's perfect).
Pour into your tray and bake for 40-45 minutes, until risen and a skewer comes out clean.
While the sponge bakes, make the sauce: melt sugar gently in a pan without stirring, swirling the pan instead. Once melted, add butter and salt, stir, then slowly pour in the cream and treacle .Simmer briefly until glossy and silky.
When the sponge is ready, poke holes all over with a skewer and pour over half the sauce to soak in. Serve warm with the rest at the table, with cream, ice cream, or custard.
