In a big bowl combine flour, sugar, baking soda and salt. Add the butter and mix using a mixer until it is all well combined.
In a small bowl whisk together the egg and buttermilk.
Start beating the flour mixture again on medium speed, and slowly add the buttermilk and egg mixture to the flour mixture. The resulting dough will be very wet.
Dump the dough onto a floured surface and knead a little to turn it into a round loaf. You might be tempted to add more flour, but don´t do it.
Place the loaf on a previously greased (or lined with parchment paper) baking sheet. Using a serrated knife, cut an X on top, as big as you want it. Sprinkle the oats on top to decorate.
Bake at 350°F (180°C) for 45 min. aprox. or until a wooden stick comes out clean when inserted.