Put the oats into a food processor and pulse until they are finely ground.
In a large bowl whisk together the ground oats, flour, baking soda and salt.
Add in the honey and buttermilk. Mix together until well combined.
Place the dough onto a lightly floured surface and use floured hands to work the dough into a smooth ball.
Melt 1 tablespoon of butter. Pour it into the bottom of a 10-inch cast iron skillet.
Transfer the dough to the prepared skillet. Use a knife to cut a large cross about ½-inch deep in the top of the dough.
Melt the remaining ½ tablespoon butter and brush it over the top of the dough.
Bake in the preheated oven for 45-50 minutes, until the bread is golden brown and the center appears cooked. If you tap the bottom of the bread it should sound hollow.
Carefully remove the skillet from the oven and let cool for 10 minutes, then transfer to a wire rack.