Combine Weet-Bix and 1/2 cup boiling water in a small bowl. Stir to make a porridge, and set aside. Combine So Good milk and 1/4 cup boiling water in a large bowl – the liquid should be room temperature, not hot. Add honey and sprinkle over yeast, stirring well. Set aside 5 to 10 minutes until foamy – this means your yeast is alive.
2. Add Weet-Bix porridge and oil to the yeast mixture. Stir, with a large spoon or scraper, then add the white flour, wholemeal flour, 1 tsp cinnamon, and salt. Mix well, using clean hands if necessary, to create a shaggy dough with no visible dry ingredients.
3. Cover bowl and rest for 10 mins, to allow the dry ingredients to hydrate – this makes the dough much easier to knead. Dust bench-top lightly with a bit of extra flour and turn dough out of bowl. Knead 3 mins, adding a pinch or two of extra flour if necessary. The dough should be smooth and elastic.
4. Flatten dough into a rough round, sprinkle over remaining 1 tsp cinnamon and the diced apple. Roll to enclose apple in the dough, and knead a further minute or two to evenly distribute.
5. Drizzle about a teaspoon of extra oil into the mixing bowl, add dough, and turn to coat. Cover bowl with plastic or a damp tea towel, and leave to rise in a warm place until doubled in size, roughly 1 hour.
6. Punch down dough, divide into 12 even pieces and form into balls. Line an oven tray with baking paper and arrange buns on the tray, leaving about 1 cm between each. Cover tray with plastic or a damp tea towel and leave buns to rise until nearly doubled, 30 - 45 mins.
7. During the last 15 minutes of rising, preheat oven to 180°C (355°F). In a small bowl, combine flour and water for the crosses and stir to create a thick, smooth, paste. Spoon paste into a small piping bag and pipe crosses onto buns.
8. Bake 22 - 25 minutes, until golden. Cool slightly on tray, then transfer to a rack and brush with warm honey, if using.