Why and how you should use this technique

What’s fantastic about this method, besides its clear speed and minimal equipment requirements, is the very limited margin for error. Mary Berry herself refers to it as "a simple, simple, foolproof way of doing it" during a masterclass for the third season of the BBC series "The Great British Bakeoff."
In fact, your biggest challenge will be ensuring the water reaches the correct temperature. Berry provides some useful guidance, suggesting it should feel "sort of like the temperature of a baby's bath." If you follow her advice, you'll achieve butter that is "squidgy and soft, just the right temperature for the creaming method." And if you want to gather more of her insights on using butter in your baking, be sure to check out another one of her top tips for making exceptional cakes.
One of Berry's preferred uses for this perfectly softened butter is in cakes, such as a classic Victorian sponge. However, you can also use it in other recipes that require creamed butter and sugar, like chewy coconut chocolate chip cookies. There’s nothing stopping you from applying this technique when you want to simply butter some bread, create a delightful butter board, or make your own compound butter (butter infused with additional flavors) for steaks, baked potatoes, and similar dishes. With so many possible applications, this is one trick you definitely shouldn’t forget.
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