How to Make It
Preheat oven to 350°F.
In an 8-inch cast iron skillet (a 10-inch skillet will work as well, though it will result in a slightly thinner cookie), melt butter over medium-low heat. Add sugar and vanilla, stirring with a rubber spatula. Remove from heat and let cool for 10 minutes. Whisk in the egg.
Add the oats, flour, baking soda, cinnamon, espresso powder (if using), and salt to the skillet and stir to combine. Using your hands, crush ⅔ cup Cracklin’ Oat Bran into small pieces. Stir into the pan. Fold in the raisins. Use a rubber spatula to smooth out batter so it is evenly spread across the pan. Sprinkle the remaining ⅓ cup whole Cracklin’ Oat Bran pieces over the top of the batter.
Bake until the edges are golden brown but the middle is still soft, about 17 minutes. Serve warm with vanilla ice cream.