Preheat the oven to 450 degrees F.
In a large bowl, combine the 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 center of the dry ingredients and pour the wet ingredients into the well. With your fingers, a spatula or wooden spoon, stir the batter from the middle of the bowl to the outside, until it’s well mixed. It will look more like cake batter than bread dough.
Brush a 9×5×2 1/2-inch loaf pan with melted butter. Pour the batter into the prepared pan and sprinkle the top with oats.
Put the bread in the oven, immediately turn the temperature down to 400 degrees F. Bake for 45 minutes, until a toothpick comes out clean. Turn the bread out onto a baking rack and allow to cool completely. Slice and serve with salted butter, toasting slices in a toaster oven if desired.