The amazing thing about this frosting is that while it looks like a standard seven-minute frosting it behaves much, much differently. Whereas seven-minute frosting hardens to a stiff meringue-like consistency almost immediately after it’s made and applied, this stays smooth and spreadable — even after several days in the refrigerator. That makes it somewhat dangerous since leftover frosting is wicked good on a vanilla wafer, or two, or three…
On a cake colonnade frosting sets up after about twenty minutes, and while it may form a thin crust, underneath it remains soft. As for why this frosting is named for a row of columns in a classical Greek structure, I can’t say. Start by assembling your ingredients. Combine the sugar, corn (or glucose) syrup in a small saucepan and bring it up to 238 degrees Fahrenheit (soft ball stage).
Meanwhile, put the whites in the bowl of a mixer fitted with the whip.
Whip to stiff peaks. I nearly overdid it here. These are maybe a little too stiff for comfort…they’re nearly dry, and dry is not what you want.
When the syrup is up to temperature quickly transfer it to a glass measure or some other convenient pouring device. With the machine off, pour about an ounce of the syrup in. Turn the machine on high for ten seconds. Turn it off, add another ounce of syrup, turn it to high for 10 seconds, you get the idea. The frosting will increase in volume and silkiness.
Lastly whip in the powdered sugar (and any colorings or flavoring you’d like). The powdered sugar adds body and, I believe, the small amount of corn starch works as a dessicant to keep the frosting from weeping.
Use right away or store in the refrigerator for later.