Put the bread flour, baking powder, cinnamon, nutmeg, mixed spice and 1½ tsp of salt into a bowl. Mix to combine, then set aside.
Put the yeast, 10g of the dark brown sugar and 50ml of lukewarm water into a small bowl, and mix. Once the yeast and sugar are dissolved, set aside and allow the yeast to ferment for 30 minutes. Put the butter, remaining sugar, treacle, vanilla, Guinness and fermented yeast mixture into a pan over a low heat, and stir until the butter has melted and the sugar has dissolved, then set aside to cool.
Add the raisins, mixed peel, glacé cherries and ginger into the flour mix and combine, ensuring the fruits are evenly distributed throughout. Add the egg, orange zest and juice, and gravy browning (if using) into the mixture and slowly stir together. Gradually pour in the cooled sugar-Guinness mixture. Mix well until you have a smooth, silky brown batter.