Warm the Guinness gently so it is just lukewarm, not hot. Stir in the treacle and honey until loosened and glossy.
Sprinkle over the yeast and leave it for 5 to 10 minutes until it starts to foam slightly.
In a large bowl, mix the flours, salt and bicarbonate of soda. Pour in the stout mixture and add the butter, then bring everything together into a sticky dough.
If it feels too wet, add extra flour a little at a time until soft but manageable.
Knead for 8 to 10 minutes until smooth and elastic. The dough should still feel slightly tacky.
Cover and leave somewhere warm for 1 to 1.5 hours until doubled in size.
Knock the dough back and divide into 8 equal pieces. Shape into rolls and place onto a lined tray.
Cover and leave to prove again for 40 to 60 minutes until puffed.
Brush lightly with Guinness or honey and scatter over oats if using.
Bake at 180°C fan for 18 to 22 minutes until deeply coloured and hollow sounding underneath.
Brush the warm rolls lightly with a little warmed treacle or honey as they come out of the oven.
