Preheat oven to 220 C. Grease a 20cm square cake pan.
Mix together the oats, flour, sugar, soda, baking powder and salt in a large bowl. In a large jug, stir together the butter, vanilla, buttermilk, and stout.
Gradually stir the liquid mixture into the flour mixture until smooth. Pour batter into the prepared pan and sprinkle with extra oats.
Bake in oven for 30 minutes and then reduce the oven temperature to 200 C. Bake for an additional 30 minutes. Turn the oven off, open the door, and allow the bread to cool for 30 minutes in the oven before turning out onto a wire rack.