From America's Test Kitchen Season 9: Old-Fashioned Snack Cakes
While we (usually) love the broiled icing on this classic snack cake, we find that the cake itself is often dense, gummy, and bland. And the icing isn’t always perfect, either; it can be saccharine sweet and tend toward greasiness. We wanted a moist, not dense, cake with buttery undertones topped by a broiled icing that features chewy coconut, crunchy nuts, and a butterscotch-like flavor. We solved the problem of denseness by replacing some of the brown sugar with granulated sugar—less moist than brown sugar, granulated sugar lightened the cake’s texture. We also reduced the proportion of flour to oats, using the minimum amount of flour needed to keep the cake from collapsing into crumbs.
The cake was now sufficiently light, and its more moderate sweetness made it better suited to a sugary icing. We still had to tackle the gumminess, however, which was created partly by soaking the oats in water; the hydrated oats were a sticky mess when we stirred them into the batter. But simply folding in dried oats didn’t work—they never fully hydrated during baking, and tasted raw and chewy in the finished cake. The answer proved to be soaking the oats in room-temperature rather than boiling water, minimizing the amount of released starch.
As for the type of oats, quick-cooking worked best. Unlike the cake, the icing only required a few tweaks. Cutting back on the sugar brought the sweetness in line, using melted butter (rather than creaming the butter into the sugar) simplified the recipe, and adding a splash of milk made the icing more pliable. Keeping the cake about 9 inches from the heating element produced the “crun-chewy” texture we wanted.
Makes one 8-inch square cake
Do not use old-fashioned or instant oats for this recipe. Be sure to use a metal baking dish; glass pans are not recommended when broiling. If you have a drawer-style broiler (underneath the oven), position the rack as far as possible from the broiler element and monitor the icing carefully as it cooks in step 5. A vertical sawing motion with a serrated knife works best for cutting through the crunchy icing and tender crumb.