Perhaps because when I read the recipe, I realized it was no regular cake. The Brown Butter Hazelnut Cake's roots are in dacquoise. Traditionally, dacquoise is defined as nut meringue. These edible architectural details can usually be found demurely hiding in between layers of buttercream as they start out crunchy but softly melt into a layer of sweet nutty unctuousness.
Easy on paper, the meringue (French, Swiss or Italian) is a component which can frustrate even the most seasoned baker. When recipes rely on egg whites or meringue as their main leavener, the workings and instructions of the recipe are very important. Few cookbooks can afford to take the time to explain thoroughly what I am about to here.
In the following step-by step photographs, I hope to answer some of the many questions people ask me about meringue and the recipes which are built on/around them. The hints and advice outlined here can be applied to mousse, buttercream, angel food cake, tortes, semifreddo, molten chocolate cake, quenelles, Pavlova and many more.
When making meringue, we start with room temperature whites. This is because egg whites are pure protein and we want to coax them into doing what we desire them to do. Just as we would not put a very cold piece of meat in a very hot pan. Because a meringue is built, not merely made, we don't rush. They must be completely free of yolks and the bowl they are cracked into needs to be intensely clean. We create a meringue with patience and thoughtful watchfulness. One egg white can quadruple in size and become all the structure a strong protein will, if it feels respectfully cajoled. This is the same idea as kneading bread to activate gluten. Gluten is the protein in flour which gives bread structure.
We start with the freshest eggs. The younger the hen, the stronger the egg white.
The best way to make a meringue is with a stand mixer. Because unlike you or a hand-held mixer it can aerate better, with more force more evenly. Start on the slowest speed and over time increase your speed incrementally. Never stop the mixer in the middle of making the meringue. Like taking a horse across a river, stopping midway will break the momentum and you and horse will be taken down the river by the strong current.
The above photo shows "trails" made by the whisk, notice that the whites have started to become shiny. In the case of a French meringue, we would add the sugar now, a little at a time, so as not to overwhelm and demolish the cloud-like body of the egg whites. This is why superfine sugar (aka baker's sugar or bartender's sugar) is recommended for meringue or baked goods with fine crumb.
Never add anything to the meringue before you have created some body. (Even though the instructions in this recipe say differently.) Otherwise, as with whipped cream, you will weigh down the liquid and it will not fluff properly.
In this recipe you have three mixtures to contend with. One bowl of drys: confectioners sugar blended with nuts and a scant amount of flour, liquid brown butter, and your strong but fragile meringue. Because these mixtures are completely disparate and threaten to cancel each other out, it is of utmost importance that they be added together carefully, gently and intentionally.
In another small bowl on the side, use a whisk to mix a small amount of the meringue with some brown butter. As when making a vinaigrette, you want to fool two ingredients that would normally repel each other into melding together. You are creating an emulsion ( = liason) here so that blending the larger quantities will be an easier, more accepted transition between all parties.
With a wide malleable spatula this mixture gets scraped into the larger body of meringue with another splash of brown butter. Turn the bowl so as to push the spatula down to the bottom middle of the bowl and fold layers under-over. A few strokes before it's uniform, sprinkle about a cup of drys over the entire surface of the young batter. With a few streaks of drys still visible, repeat with brown butter and drys just until batter is uniform.
With dacquoise this dry-wet pattern should be gentle and careful but not excessive. Overmixing, although it looks and feels impossible to do so, may eradicate all those tiny little air bubbles which you worked so patiently to build.
In the microscope of your imagination what you are creating is a very thin fine coating of sugar around the millions of tiny egg white bubbles. This is what creates the crispy crunchy meringue.
This particular recipe is very high in fat not only because of the quantity of the brown butter, but also because of the state it comes in. Liquid. When we use the "creaming method" as in the average American cake or chocolate chip cookie, we rely on the fact that a stick of butter is not pure fat. It has water and milk solids that are perfectly homogenized into the butterfat. But when we brown butter we are "clarifying" it -- meaning that the water evaporates and the solids crystallize.
Making dacquoise, like mousse, is about the tenuous balance of fat and that which binds it. These emulsions are very precarious. Your final mixture may look "broken" but do not fear! Meringue does not kiss and tell. If you get it perfect it's like the basketball whooshing into the basket with no one to see.