Preheat the oven to 200°C fan. Grease and line a 2lb loaf tin.
Add the wholemeal flour, plain flour, porridge oats, salt and bread soda to a large bowl. Mix well, making sure there are no little lumps of bread soda.
Place the treacle in a jug and mix it with a small splash of the buttermilk to loosen it. Pour in the remaining buttermilk and Guinness and stir everything together.
Add the wet ingredients to the dry ingredients and mix gently until just combined. The mixture should be wet and spoonable,
Add into the prepared tin, smooth the top and sprinkle over a few extra oats.
Bake at 200°C fan for 15 minutes. Reduce the temperature to 170°C fan and bake for another 45–50 minutes.
Insert a metal skewer deeply into the centre it should come out clean, without any wet mixture.
If needed, give it another 5–10 minutes, covering the top loosely with foil if it’s already dark enough.
Leave the bread in the tin for 15 minutes, then transfer it to a wire rack. Allow it to cool for at least 45 minutes before slicing, if you can resist it!
Serve thickly sliced with plenty of real Irish butter.
