Preheat oven to 450°F.
In a large bowl, mix oats, whole wheat flour, all-purpose flour, brown sugar, baking soda, baking powder, and salt.
In a separate bowl, whisk together the beer, buttermilk, melted butter, and vanilla.
Make a well in the dry ingredients, and pour the wet ingredients into the well.
Stir the batter from the middle of the bowl to the outside until it's well mixed. It should look like a cake batter rather than a typical bread dough.
Grease a 9-in. x 5-in. x 2½-in. loaf pan with butter or cooking spray. Pour the batter into the pan and sprinkle the top with rolled oats.
Place the bread in the oven, and immediately turn the heat down to 400°F.
Bake for 45 minutes, until an inserted toothpick comes out clean.
Turn the bread out onto a cooling rack, leaving it to cool completely.
Slice and serve with salted butter; Irish Kerrygold pairs very well, if you have it.