The fat in butter is partially crystalline and highly sensitive to temperature changes. When butter is properly softened to 65 or 70 degrees, the tiny crystals can effectively surround and stabilize the air bubbles that are generated during creaming. When heated to the melting point, however, these crystals are destroyed. They can be reestablished but only if the butter is rapidly chilled. (Returning it to the refrigerator will cool it too slowly and fail to reestablish the tiny crystals.) To quickly cool down partially melted butter, we mixed in a few ice cubes. After less than a minute of stirring, the butter had cooled to a softened stage—right below 70 degrees—so we extracted the ice and prepared a couple of recipes. (The amount of icy water that leaked into the butter was negligible.)
OUR FIX WORKED: Sugar cookies made with our rehabilitated butter were nearly identical to those made with properly softened butter, and buttercream frosting was also acceptable, if slightly softer than a control batch.
