Okay, now don’t freak out, but there is mayonnaise in this cake. I know: crazy. But it takes the place of the oil in the recipe, as well as the eggs (though, yes, I do throw in one, for good measure). And the texture is so perfect, as well as the flavor, that you need to put any mayo-phobias behind you and get baking. The marshmallow frosting here is epic, but if you’re just not feeling like pulling out your stand mixer for it, I totally understand and suggest you glaze this cutie with Cream Cheese Glaze instead.
In order to achieve the perfect balance of cakey and gooey—that sweet spot that all brownies should hit—the cooking time is crucial. It will vary by a minute or so depending on where the pan is sitting in the oven, so keep a close eye on them.