Preheat the oven to 180°C fan (350°F). Grease and line a 1lb loaf tin with parchment paper.
In a jug or bowl, whisk together the Guinness, sour cream, milk, and black treacle until smooth.
In a mixing bowl, whisk together all your flours, oats, baking soda, brown sugar, and salt.
Make a well in the center of your dry ingredients and pour in the wet mixture. Gently mix until just combined.
Transfer the dough to your prepared loaf tin, using a spatula to smooth the top. Sprinkle some more oats over the top.
Bake for 42-45 minutes, or until the loaf is firm to the touch and sounds hollow when tapped.
Remove the loaf from the tin 10-15 mins after taking it out from the oven, and let it cool on a wire rack before slicing.
