Make the starter mixing together the water, yeast, sugar, egg yolk and plain flour in a bowl. Cover and leave to rise for 2 hours.
Combine the starter with dough additions 1 either in a bowl or using a stand mixer. Knead by machine, or in the bowl by hand for 10 minutes. Transfer to a lightly greased bowl, cover and leave to rise for 2 hours.
Add the dough additions 2 to the dough and combine together well. Knead for 10 minutes by machine. Transfer the dough to a bowl with a little oil, turning it to coat. Cover and allow to rise for 2 hours.
Prepare a 10” bundt tin by greasing and flouring. Take the risen dough from the bowl and add it to the prepared tin, stretching it to fill the ring. Cover and leave to rise for 1 ½ hours. Preheat the oven to 180c (fan)/200c/ Gas Mark 6.
Bake in the oven for 40 minutes. When baked, release it from the tin and allow to cool on a wire rack. Combine the icing sugar with the orange juice, just a little at a time to create a thin glaze. Trim the base from the Pandoro so that it sits level and gently over the glaze.