Preheat oven to 375 F. In a large bowl combine the oats, flour, sugar, salt and baking soda. (If you are making the cocoa version add the cocoa and coconut here)

Add the butter and using a large fork, pastry blender or your fingers,  work the fat into the dry ingredients.

Pour in the boiling water and stir until everything comes together into a thick, sticky dough.

On a large baking sheet, like a 15 x 10 or a 13 x 9 pan, press the dough directly onto the sheet using a metal spatula to flatten the dough into an even 1/4″ layer.  Score into small squares. They will blend together when baking, but will be easier to cut if you do this before baking.

Bake until golden, about 12 minutes. You can take them out of the oven now but if you prefer a chewier oatcake reduce the temperature to 325 and bake until lightly browned, about 10 more minutes.

Remove from oven and cut them apart while warm. Place on a rack to finish cooling.