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When Tragedy Strikes Your Mousseline Buttercream

May 7, 2016 | From the kitchen of Rose


This is truly the queen of buttercreams: silky, buttery, light and airy, and a bit temperamental. Combining the Italian meringue with the butter is the tricky part. It is essential that the two mixtures have near the same temperature. And sooner or later it happens to everyone: Instead of becoming a beautifully emulsified satiny texture, it starts to curdle and separate. Your heart drops and panic sets in--all that expensive butter and time....But all is not lost. Here are some tips and also a solution should all else fail:

Use an instant read thermometer to ensure that the temperature of the mixture is between 65° to 70°F/19° to 21°C and adjust as needed. If not using a thermometer, try adjusting with just a small amount of the buttercream.

If all else fails, with your hands, squeeze out the liquid that has separated and pour it into a large measuring cup with a spout. On high speed, beat the remaining butter until it becomes smooth. Then gradually beat in the liquid. The resulting buttercream will be less airy but perfectly emulsified and silky smooth.

Note: You will have a higher degree of success if using high fat butter.
Also, it works best to add all the meringue to all the whipped butter rather than the reverse. This technique is detailed in Rose's Heavenly Cakes and The Baking Bible.



Hi Suzanne,
We think you will not have a problem as you are bringing honey to a rolling boil which is the same as the Neo-classic Buttercream with the temperature or water content.
With your experience and a few small test batches, we think you can easily find good results. You could try calling the Johnson & Wales culinary school in Denver for what they may know, or check some of the Craftsy on-line classes, since their studio is in Denver.
Rose & Woody


Suzanne Forbes
Suzanne Forbes
09/ 7/2016 10:01 AM

Hi folks- I am a longtime devoted fan, and have made Rose's Royal Honey buttercream hundreds of times.

Next week I'm making a wedding cake in Santa Fe, at 7,500 feet. I bought "Pie In the Sky" as Rose recommends, but I really want to make honey buttercream as the filling.

I read all the posts about sugar boiling temperature adjustments and sugar syrup moisture content, but can't figure out how the difference will translate. Any tips? Thanks a million!


Ohhhhh... I used the whites to make the White Chocolate cake! :) I remember the last time I made it, it was somewhat dry, so before putting it together this time, I put a mixture of simple syrup and a white chocolate liqueur on it! The liqueur made it incredible!! It's a great combination with the raspberry buttercream, if it wasn't so soft....lol. I got quite a few compliments on it!! :)


Hi Joyce,
It sounds like your butter was too soft when you added it to the sweetened yolk mixture. The butter should be between 65 and 75F, but if you are it making it in a a hot and/or high humidity kitchen, then the butter should no higher than 70F. Once cooled to a cool room temperature, it should be fluffy and hold whatever pattern you design.
If you have not tried it, we suggest making the Mousseline Buttercream with all the leftover whites. However, use the recipe technique in "Rose's Heavenly Cakes" or "The Baking Bible" for making it.
Rose & Woody


Hi Rose.....

I have a question for you. It's been a long time since I made your neoclassical raspberry buttercream that was featured in the July 1988 issue of Chocolatier Magazine. I tried making it again last week and although the taste was incredible, it was really really soft!! It was so soft, that when I cut the cake, it looked as though it melted into the cake a bit and the top sort of slid off a few times. I even refrigerated it for a while, thinking it would harden a bit. What causes this? Was the butter too soft? I didn't know what to do, so I just sort of laughed it off.


I read somewhere that melting a small amount in the microwave (about a 1/4 cup) and then beating it in to the curdled buttercream works well, so I actually tried it... Worked perfectly :)


Hi Ruth,
We have used meringue powder for royal icing, but we have not used it for mousseline since it has a 2 day room temperature storage time. However, in the past, I have entered frosted cakes at a state fair and although judging was done within 24 hours of delivering my entries to the fair, we understand your uncertainty.
We recommend you try making a small batch of egg white mousse line and another with the meringue powder to compare.
Rose & Woody


Hello, Would like to use the Raspberry Mousseline recipe on chocolate cupcakes. Is it possible to make the meringue with meringue powder I use to make royal icing? It's for a local fair and I'm afraid the judges may not even try it in this heat because of the fresh egg whites. They may not want to chance it. Thanks so much.


Printing and posting all these tips on the inside of my kitchen cupboard door!


Hi Orin,
In "The Cake Bible", Rose gives some basic instructions for preparing a cake's surface with a thin smooth layer of buttercream or melted jelly for the fondant to adhere to it. In "The Baking Bible", The Pink Pearl Lady Cake has more detailed instructions for preparing the mousseline buttercream undercoating and applying the fondant on pages 46 and 47. The undercoating should be thin and smooth for the fondant to look smooth and wrinkle free. Once applied, the undercoated cake should be refrigerated until the mousseline is firm.
Rose & Woody


love this butter cream,as I use it my to go one for almost any cake. and like probably everyone els it happen to me when the butter melted, but it made me to never repeat it again and watch the temperature carefully.

my question is: how to apply a fondant on this type of buttercream? while it cold or allow the buttercream rest to room temperature and than apply the fondant?

much thanks


Patricia @ ButterYum
Patricia @ ButterYum
05/ 7/2016 12:56 PM

It has only happened to me a few times, but I've found placing the entire bowl of broken buttercream (whip and all) into the fridge to chill for about 5 minutes seems to do the trick. When I put the bowl back on the mixer, all is right with the world.



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