To prepare a worlds best maine whoopie pies recipe, first you need to gather your ingredients. First, you'll need the following ingredients: 1 pound rolled oats, 1 cup brown sugar, 2 tablespoons butter, and 1 teaspoon vanilla extract. Mix the ingredients together until they're evenly combined. Then, pour the mixture into an oiled 9x9-inch baking pan and bake for 20 minutes. Remove the pan from the oven and allow it to cool for 5 minutes before slicing it into bite-sized pieces.