Preheat the oven to 200C/gas 6/fan 180C. Butter 6-8 muffin tins or line them with muffin cases. Put the flour, oats, sugar, cinnamon and bicarbonate of soda in a large bowl, then rub everything through your fingers, as if making pastry, to ensure the ingredients are evenly blended.
Beat the egg, then stir in the buttermilk, vanilla and oil. Lightly stir the egg mix into the flour.