Soak the chopped dates in the hot brewed tea and set aside to cool for 20 minutes.
Preheat the oven to 160°C (fan). Butter and lightly flour a rectangular deep pudding tin (such as a 16 x 12" enamel pie dish), tapping out any excess.
Beat the butter and light brown sugar together until light and fluffy, gradually adding the eggs one at a time.
Mix in the vanilla and golden syrup.
Fold through half of the dry ingredients (plain flour, cinnamon, salt, baking powder, and bicarbonate of soda) and half of the milk, mixing well. Then fold in the remaining dry and wet ingredients.
Fold through the date and tea mixture along with the chopped walnuts. The batter might look a little curdled — this is perfectly fine.
Pour the batter into the prepared tin and bake in the preheated oven for 45–50 minutes. Check at 40 minutes — if it still looks too raw, bake for another 5 minutes. Try not to overcook, as this is a moist sponge.