Preheat oven to 350 degrees F.
Place oatmeal in a blender and pulse a couple of seconds until the oatmeal is ground. Place in a bowl.
Add in the flour, brown sugar, baking soda and salt.
Cut in the butter with your fingers until the mixture resembles course meal and the butter has been mixed in.
Add in the hot water, and with a spoon mix into a ball.
Place on a lightly floured work surface and roll out into desired thickness. Cut into rounds, or into squares. If there is any leftover, roll out again and cut.
Bake in the preheated oven for about 13 minutes, then flip each over and return to oven for about 2-3 minutes more, until the oatcakes are crisp and light browned.
Let them cool, and enjoy.