Mousseline Buttercream

It’s amazing to me that combining whipped butter and an Italian meringue (egg whites whipped with sugar and cream of tartar, to which a hot sugar syrup has been added) results in something this light, this silky, yet this creamy. This is a frosting I use often for its stability, its versatility and the ease with which one can work with it.

As with most of Rose’s recipes, if the detailed instructions provided are followed and ingredients measured accurately, success is assured.

The base recipe is not very sweet and the author provides instructions for a number of flavour variations, but really, the flavours that are possible are limited only by your imagination. I made the white chocolate variation for my most recent cake, the white velvet butter cake, also from The Cake Bible.

This buttercream is silky smooth, rich and not too sweet, which means I'll never again suffer through gritty or overly sweet powdered sugar frostings. It's bascially whipped butter lightened with Italian Meringue. It is a little more challenging to make than a powdered sugar frosting, but very worthwhile to master.

There is an updated technique on the author's Youtube video, which basically involves dumping all of the cooled meringue onto the whipped butter at once and then whipping at med-high or high speed. This is much faster and simpler than the tablespoon-at-a-time method in the book, and I've done it several times now, it works well.

An important tip is that this buttercream almost always curdles a little bit just before it forms an emulsion- keep beating on med-high or high and as long as it's at the right temperature it will come together. The ideal temperature for both the whipped butter and the cooled meringue is about 70F.

If the temperature of the buttercream is too cool and it curdles, even badly, it can still be saved by bringing the mixture to the correct temp and then beating on high speed.

Another point is to err on the lower side of the 248-250F for the temperature of the cooked sugar syrup. Going over 250F will produce an overly firm, hard-to-pipe and unpleasant-to-eat buttercream. If the sugar syrup does overshoot 250F, it's easy to swirl in a little water (the temp will lower) and then try for 248F again.

Finally, unsalted butter is a must. Salted butter doesn't taste good in this.

My favorite flavors are the lemon curd and the white chocolate. Normally, I don't care for white chocolate at all, but in this buttercream it doesn't come across as too sweet and it does something incredibly dreamy to the texture.

The photos show a cake frosted with lemon curd mousseline, and cupcakes frosted with white chocolate mousseline.