The night before, put the dried fruit in a large bowl with the tea bags and cover with the boiling water. Leave to cool, then soak overnight so the fruit plumps up in the cold tea.
The next day, heat the oven to 170C (150C fan) and line a 900 g loaf tin with baking paper.
Lift out the tea bags, then stir the sugar, egg, golden syrup, mixed spice and salt into the soaked fruit along with all of its tea.
Sift in the flour and fold it through until just combined into a heavy, sticky dough. Add a splash of milk only if it refuses to come together at all.
Spoon into the tin, level the top and bake for about 1 hour, until a skewer pushed into the middle comes out clean. If the top darkens before the middle is done, cover it with foil.
Cool in the tin for 10 minutes, then turn out onto a rack. It slices best on day two, and proper bara brith is eaten thickly buttered.