Something that I can’t stress enough when it comes to baking any kind of egg-enriched cake (layer cakes, muffins, doughnuts, tea breads, pound cake, you name-it) is that your eggs must be warm before you begin. Why? The answer is that a cake batter is an emulsion, which is to say, a matrix of tiny fat blobs dispersed in a watery medium. That emulsion plays a critical role in leavening the cake, and in maintaining its soft, creamy texture.
Emulsions are rather tricky things, as anyone who’s ever broken a Hollandaise knows. Once you establish one, it tends to want to separate into its base components again. That is, unless there are certain other chemical compounds present, so-called emulsifiers, that surround the fat blobs with protective coats to keep them from merging back together.
In a cake batter, those emulsifiers come from eggs, especially the yolks which are rich in low-density lipoproteins (LDL’s) and high-density lipoproteins (HDL’s). But LDL’s and HDL’s don’t work very well when they’re cold. Cold makes them sluggish, which makes it hard for them to form those protective layers. An unemulsified batter is extremely thin and prone to “weeping”, and results in a flat and crumbly cake.
That said, it’s best to take your eggs out of the refrigerator at least an hour before you begin mixing up your batter (2 is better). Failing that, you can put your cold eggs in a small saucepan, pour hot tap water over them, and let them sit 10-15 minutes. Applying a blowtorch to the bowl of your mixer as it runs is another way of warming up your batter, just keep clear of the drapes.