The key to chewy brownies is the ratio of saturated to unsaturated fat. I use lard in this recipe to make them dairy free. Lard is also cheaper than butter in my area. The key to the crackly tops is creaming the lard & powdered sugar, and then beating thoroughly after the eggs and oil are added. The powdered sugar is to ensure that the sugar fully melts in the oven and it being creamed and whipped makes the top bake like a meringue and end up shiny and crackly. I also keep them simple with really basic gluten free flours, so you don't have to buy any expensive blends. You can use whatever plain gluten free flour your have on hand (white rice flour, brown rice flour, sorghum flour, etc). You can also use whatever starch you have on hand (corn starch, tapioca starch, arrowroot starch, etc), and whatever neutral tasting oil you have on hand. This recipe also uses cocoa powder to save cost.