Gather the ingredients. Position a rack in the center of the oven and heat to 375 F.

In a large bowl, combine 2 cups rolled oats, 1 cup all-purpose flour, ¾ cup lightly packed brown sugar, 1 ¼ teaspoons fine sea salt, and ¼ teaspoon baking soda. Add ¾ cup shortening or butter and use 2 knives, a large fork, or your fingers to work the fat into the dry ingredients until well combined.

Add ¼ cup boiling water and stir until everything comes together into a thick, sticky dough.

You can roll the dough out on a well-floured surface, cut it into shapes, and set them on a large baking sheet. Or keep things simple, and with damp hands, press the dough on a parchment-lined baking sheet into a 9 x 11-inch rectangle, about ¼-inch thick. Score this large 'cake' into smaller pieces: Use a serrated knife to cut the dough into squares or rectangles or whatever shapes you like, but don't bother to separate the pieces; the pieces will bake back together but be easy to cut or break along that original cut line.

Bake until the top of the oatcakes are dry and lightly brown, 13 to 15 minutes. You can take them out now for chewier oatcakes or for a crispier version, reduce the oven temperature to 325 F and bake 5 minutes longer.

When they have finished baking, if you've cut them into shapes, let them cool; if you've scored them, cut them apart while warm so they cool into squares (or rectangles or triangles or whatever you've cut them into).