Heat oven to 180°C (160°C fan). Butter the tin, add the demerara, shake to coat and tap out the excess.
Steep the tea bags in the water for 4 mins, squeeze and remove. Simmer the dates in the tea for 5 mins until very soft. Off the heat, stir in the bicarb (it will foam), blend fairly smooth and cool slightly.
Beat the butter and dark muscovado for 3 mins until fluffy. Beat in the eggs one at a time, then the golden syrup, treacle and vanilla.
Fold in the flour, then the milk, then the date puree. It will look far too runny; that’s exactly right.
Bake for 25 to 30 mins, until a skewer comes out clean.
For the sauce, warm the cream until steaming, steep the tea bag for 5 mins, squeeze and remove. Melt the butter and light muscovado, add the golden syrup and treacle and bubble for 2 to 3 mins until glossy. Add the cream in two batches, then simmer gently for 5 mins until slightly thickened. Stir in the salt.
Poke holes all over the hot sponge. Pour over a third of the sauce, leave for 5 mins, then bake for 5 more mins until bubbling at the edges.
Rest for 10 mins, slice and serve with more sauce and vanilla ice cream.
