Combine flour, soda, salt, and 3 tbsp oats in a bowl; cut in butter
with a pastry blender until mixture is crumbly.
Combine egg, buttermilk, and brown sugar; add to flour mixture, stirring
with a fork just until dry ingredients
are moistened.
Spread dough in a greased 9" cast iron skillet. Sprinkle with
remaining oats.
Bake at 425 for 25 minutes.
Cut into wedges; serve warm with preserves.
Yield 8 servings.