In a large bowl, stir together the oats and buttermilk and let sit about an hour.
Preheat oven to 400°F and line 12 muffin tins with paper liners.
Add the egg, brown sugar and oil or butter to the oat mixture and stir well. Add the flour, baking powder, baking soda and salt and stir until almost combined; add any additions you like and stir just until blended.
Divide the batter evenly among the prepared muffin tins and bake for 20 minutes, or until golden and springy to the touch. Serve warm.