Squishy butter
Yes, it’s a thing! Squishy butter is just what you want when creaming butter for a cake or sponge. It’s the first step to ensure that sugar will mix with the butter and ‘cream’, forming a light and fluffy base that will absorb egg yolks, which are also fat-based, when added. There is no way you will successfully cream butter and sugar together if the butter is too firm or cold (and therefore, the mixture will split when egg yolks or whole eggs are added). If that happens, you can continue with the cake, but it will have lost considerable air, and the result will be a heavier, denser cake (but sometimes that’s what you have to do instead of throwing out the ingredients).
But all you need to do to start in the right direction is to squish the butter! Bring it to room temperature, cut it into small pieces, and leave it at room temperature in a warm kitchen for an hour or so. Sometimes, I know, we can’t wait that long; you can use a microwave but with caution. Soften the butter in increments. Try 7 seconds to begin until you get a feel for it. Whatever you do, don’t melt it. Why? Because melted butter is liquid and cannot hold air.
Another tip to encourage the creamed butter and sugar to absorb the egg yolk is to ensure the egg yolks are at room temperature. When the two fats are at the same temperature, they will mix more readily than when mixing cold egg yolks into soft butter.