French Mousseline Buttercream

I can tell I am getting wound up about the upcoming royal wedding when I have buttercream on my mind. Mousseline Buttercream are two sweet words that slide off the tongue.

Also called a French buttercream or Swiss buttercream, leave it to the French to find a way to make one of the richest, most luxurious frosting preparations in all of pastrydom. How do they do that? By employing egg yolks in their classic buttercream instead of whipped egg whites (which is known as an Italian buttercream-more on that in a later post) with fresh unsalted butter and a sugar syrup. The taste and texture is pure velvet and silky on the tongue, and far superior than a powdered sugar icing. This is usually the preparation that is made for filling and icing cakes and piping on top of cupcakes when the baker says s/he made “a real buttercream”, not the one based on powdered sugar.

This is a variation on the French buttercream I learned from The Making of A Cook by Madeleine Kamman (Atheneum, 1971) as it is taught in all basic pastry courses. Cake layers can be made ahead and frozen, ready to be frosted and decorated at a moment’s notice, which is how it is done in professional bakeries.

Makes about 2 1/2 cups, enough to fill an 8-inch 3-layer cake or 9-inch 2-layer cake. The basic recipe can be doubled. You will use about 1 1/2 cups for frosting the top and sides.

Special Equipment

•5-quart stand mixer with bowl and whisk and paddle attachments

•heat resistant rubber spatula

•candy thermometer

Ingredients

• 3/4 cup sugar
• 1/3 cup water
• 3 drops fresh lemon juice
• 8 large egg yolks, room temperature
• 1/2 pound (2 sticks) unsalted butter, softened and cut into pieces

Flavoring Options (choose one-if undecided, use vanilla)

• 3 to 4 teaspoons vanilla extract
• 3 to 4 teaspoons chocolate extract (available through Williams-Sonoma)
• 3 to 4 teaspoons almond extract
• 1 tablespoon orange oil
• 2 teaspoons lemon juice plus 4 teaspoons lemon zest
• 2 teaspoons ground cinnamon
• 3 tablespoons liqueur of choice (each has a different strength, so only add enough for a hint of flavor. Best used the day it is mixed.)
• 2 tablespoons espresso powder dissolved in 1 1/2 tablespoons water, cooled

Instructions

1. In a small saucepan, combine the sugar, water, and lemon juice, stirring occasionally. Simmer on medium-high until the sugar is dissolve and the liquid is 240ºF to 244ºF (firm ball stage in candy making terminology) on a candy thermometer, about 4 minutes. Use a pastry brush dipped in to brush down sugar crystals from the sides of the pan.

2. Meanwhile, place your room temperature yolks into the bowl of the stand electric mixer, fitted with the whisk attachment. Whip on medium-high speed until the yolks are foamy and pale yellow. So you will have the mixer going and the sugar syrup cooking at the same time.

3. When the syrup is ready, switch to the paddle attachment and with the mixer on high speed, very slowly drizzle in a thin steady stream the syrup into the yolks until all has been added. Continue beating on high until the mixture is ROOM TEMPERATURE and thick, scraping down the sides once or twice, about 6 to 10 minutes (gives you time to split the layers and wash the dishes). You will not be able to feel any heat when you place your hand on the underside of the bowl.

4. On medium-low speed, beat in the soft, room temperature butter a tablespoon at a time, creaming the butter and incorporating it into the yolks. If using any flavoring, such as the vanilla, beat in just after you beat in the butter. The mixture will be shiny, smooth, and creamy. Refrigerate the buttercream for at least a half hour, and whip it smooth just before you use it.

Can be prepared 1 week ahead and refrigerated or frozen for 3 months covered tightly. Before using, bring the buttercream to cool room temperature and work with a large rubber spatula to smooth it out for spreading.

To split cake layers

Place the layer in the freezer for an hour to firm if possible as it is easier to cut a firm cake than a floppy fresh layer. Place on a work surface, or better yet, a lazy susan cake pedestal. With a serrated or long sharp knife make shallow horizontal cuts around the outer edge of the layer to mark cutting it in half. Now, leave the knife stationary, and rotate the cake, not the knife, slicing with the knife as you rotate. Using the cuts as a guide, carefully slice straight across the layer. When you’ve returned to where you began, gently move the knife through the center. This gets to be very simple with some practice.

To assemble a layer cake

Place the first layer, cut side up, on the serving plate. Brush all loose crumbs from the top and sides (I keep a small, clean soft pastry brush just for this). Sprinkle the top with some sort of spirits (Grand Marnier, Kahlua, Cherry Marnier, rum, Calvados, etc. depending on the flavors in your cake) or brush with warm jam, then spread first with a layer of buttercream only to about a half inch of the edge, then repeat with each split layer until you place the last on top. The best top is one of the bottom layers since it is flat. Spread a very thin layer of buttercream around the sides and over the top. This is known as the crumb coat. Then ice with the remaining buttercream.  Chill at least 1 hour.

Garnishes

Coat the sides if you like with something like ground toasted nuts, grated chocolate, or shredded coconut for visual appeal. If you have enough leftover buttercream, you can pipe rosettes on the top. You can arrange strawberry halves, whole raspberries, or nut halves around the top. Anything you like to give it a finished professional look that will match or reflect the flavor of the buttercream. The plain cake looks great with a dash of color. But if you  like piping, enhance the cake with simple borders, patterns of dots, criss-crossed lines, even some writing.