Because once you have filled your chocolate cake with Valencia Curd, you need something to frost it with – I give you Orange Mousseline Buttercream. Deliciously light and silky, flecked with orange zest and a gorgeous pale apricot color, this buttercream frosting is a show-stopper on any cake.

Like many of Rose’s recipes, this particular frosting recipe is finicky: butter temperature is critical, the simple syrup must be added in just the right way, and the whole time you are holding your breath lest the egg whites curdle and ruin the entire batch.  But, let me just say: this is the best buttercream I have ever made.  I think it’s the best buttercream I have ever eaten – and that comes from someone who doesn’t even like buttercream frosting.  Despite the finickyness of the recipe, I will so (so!) make this again.

On a completely un-buttercream-related note, the US plays England in the finals of the World Cup today. If you have any passion for soccer, or for America, or for the underdog toppling the giant – watch the game. Find it on ESPN, livestream it at work while you pretend to be sending emails, or better yet, go down to your local pub and cheer. Cheer loudly. This is the big time, folks. GO, USA!

Adapted from Mousseline Buttercream in The Cake Bible by Rose Levy Beranbaum

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Orange Mousseline Buttercream

INGREDIENTS

• 1 lb (2 cups) unsalted butter, softened but cool (65 degrees F)
• 1 cup (7 oz) sugar
• 1/4 cup filtered water
• 4 large egg whites (5 and 1/4 oz)
• 1/2 + 1/8 tsp cream of tartar
• 2 oz (about 1/4 cup) frozen concentrated orange juice, thawed to 65 degrees F
• zest of two medium oranges (about 3 tbsp)

METHODS

1. Beat the butter until smooth and creamy, about 1 – 2 minutes; set aside in a cool place.  If it is very warm in the kitchen, refrigerate.
2. In a small saucepan combine 1/4 cup water with 3/4 cup sugar.  Bring to a boil over high heat, stirring constantly until sugar dissolves.  Turn off heat but leave over warm burner.
3. Beat egg whites until foamy, add cream of tartar, and then beat at high speed until soft peaks form when the beater is raised (about 5 minutes in a Kitchen Aid stand mixer). Gradually add the remaining 1/4 cup of sugar and beat at high speed until stiff peaks form (about another 5 minutes). 
4. Return the sugar syrup to high heat; stirring occasionally. Have a glass bowl or measuring cup ready near the stove. Heat syrup until 248 degrees F (firm-ball stage) then immediately pour into the glass container to stop the cooking.  Watch the thermometer closely while cooking this; it will shoot up to temp quickly in the last stage, and if you over-shoot, the syrup will crystallize and you will have to start over (ask me how I know this!).
5. If using a stand mixer, add a small amount (1/8 cup) of the syrup while the mixer is off; immediately turn on the mixer and beat at high speed for 5 seconds.  Repeat this procedure with a larger amount (1/4 cup); then repeat again with the rest of the syrup, scraping the glass bowl with a rubber spatula.  If using a hand mixer, pour the syrup into the bowl in a steady stream, avoiding the beaters, as they will spray the syrup to the edges of the bowl, where it will harden & stick.  Beat on medium speed for 2 minutes; if not completely cool at this time, continue to beat on low speed until cool.
6. Beat in the 65 degree F butter, 1 tbsp at a time. The mixture will thin at first, but then thicken as you incorporate more & more butter.  If your butter gets too warm, put the bowl in the freezer for a few minutes to cool it back down; it should stay between 65 – 70 degrees F for best incorporation into the egg whites.  If at any time the mixture begins to look a bit curdled, stop adding butter, increase the speed slightly, and beat until smooth before adding additional butter.
7. Lower the speed and drizzle in the thawed OJ concentrate; raise speed to medium and beat for 1 to 2 minutes to incorporate.  Remove mixing bowl from stand and fold in the orange zest (zest tends to get clumped in the balloon whisk of the stand mixer).  Rebeat lightly if needed (buttercream becomes spongy on standing) but only when at room temperature; beating cold buttercream may cause it to curdle irretrievably.

Yields 4 and 1/2 cups; enough to fill & frost two 9-inch x 1 and 1/2-inch layers or three 9-inch x 1-inch layers.

OPTIONS

1. The original recipe suggested 3 ounces of liqueur instead of orange juice concentrate: Mandarine Napoleon, Grand Marnier, or an eau-de-vie. I think Chambord would make a lovely purple frosting with a delicate berry flavor.
2. In the photo above, the beads are piped with frosting to which I added about 1 cup of Valenica Curd; the large amount of zest in the curd makes the piping quite difficult (as you can see the beads came out a little messay and misshapen, due to zest clumping in the pastry tip); delicious, but perhaps better for a filling.  The original version of the frosting (used to frost the main body of the cake) has little zest and would likely pipe easier.

STORE

At room temperature for 2 days, refrigerated for 10 days, or frozen for 8 months.  Allow to return to room temperature before beating or you risk curdling the buttercream irretrievably.

SEASON

This is a good candiate for winter and early spring, since the success of the buttercream is highly dependent on the butter staying cool.  Yet, Rose tells us that once the buttercream is made, it holds up better than any other, so it may be just the thing if you must make a buttercream in July.