Set the oven temperature to 450 degrees.
Mix the oats, all-purpose flour, brown sugar, baking soda, salt, and whole wheat flour in a large bowl.
Whisk together the buttermilk, beer melted butter, and vanilla in another bowl. Make a hole in the dry ingredients and then add the wet ingredients.
Mix the batter thoroughly by moving your fingertips from the middle of the bowl to its periphery. The consistency will be more akin to cake batter than bread dough.
Apply melted butter to a 9 × 5 × 2½-inch loaf pan. Spoon the batter into the pan and top with oats.
Immediately reduce the oven temperature to 400 degrees and bake the bread for 45 minutes, or until a toothpick inserted in the center comes out clean.
Transfer the bread to a baking rack and let it cool entirely. Cut into slices and spoon salted butter on top.
