Preheat your oven to 170 degrees Celsius.
Combine all the dry ingredients in a bowl.
Gently heat the Guinness until it melts and emulsifies, then whisk in the treacle.
Pour the wet mixture into the dry ingredients and mix until just combined, being careful not to overmix.
Grease a 2-pound (1 kg) loaf tin with vegetable oil or butter.
Pour the bread mixture into the loaf tin, filling it up to three-quarters full.
