Caramel Frappuccino Cupcakes

This cupcake takes me back to my Starbucks days. I worked the opening shift in college, which meant getting there at 4:30 AM, bleary eyed and half dazed, filling the pastry case and waiting for the mob of high strung customers. I do actually kind of miss it...

This cupcake is a coffee flavored cake filled with coffee mousse and homemade caramel sauce, and topped with swiss meringue buttercream drizzled with caramel. It was a pretty big hit at work, so I suggest making it to all of you Starbucks fans.

For the Cupcakes (makes 24 cupcakes):
Recipe heavily adapted from Apartment Therapy's The Kitchn

3/4 cup whole or low-fat milk
1/4 cup sour cream
3 heaping teaspoons instant coffee
1 tbsp vanilla
3 cups cake flour
2 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1 teaspoon salt
2 teaspoons very finely ground coffee
2 teaspoons unsweetened natural cocoa powder
3/4 cup butter at room temperature
1 1/2 cup white sugar
4 eggs, yolks and whites separated

Heat the milk in the microwave or on the stove until hot - stop short of a simmer. Stir in the instant coffee until well blended. Add the vanilla and set aside.

Sift together the cake flour, baking powder, soda, salt, ground coffee and cocoa.

In the bowl of a stand mixer, beat the butter and sugar with the paddle attachment until creamed. It should be slightly fluffy. Beat in the egg yolks one at a time.

Add 2/3 of the flour mixture and the sour cream. Add the remaining flour mixture and milk. Beat until smooth.

Scrape all the batter out into a separate bowl and wash the mixer bowl thoroughly.

Switch to the whisk attachment and beat the egg whites until stiff but not dry. They will hold a stiff peak but they will still slip around a little in the bowl.
Fold the egg whites into the cake batter gently, folding the batter around until well combined.

Fill cupcake liners with batter and bake at 350 degrees for about 20 minutes (they baked up surprisingly fast).

For the Coffee Mousse (Recipe from Epicurious)

3/4 cup plus 2 tablespoons sugar
6 large egg yolks
1/3 cup water
3 tablespoons instant espresso powder
1/2 teaspoon ground nutmeg

2 1/2 cups chilled whipping cream
2 tablespoons coffee liqueur
1 teaspoon vanilla extract

NOTE: I cut the above recipe in half by eyeballing it (a lot of the measurements don't make for an easy division). I also used Starbucks Via Instant Coffee instead of instant espresso and cut out the nutmeg.

Whisk sugar, yolks, water and espresso powder in large metal bowl. Set bowl over saucepan of simmering water (do not allow bowl to touch water); whisk until candy thermometer registers 160°F, about 3 minutes. Remove bowl from over water. Add nutmeg. Using electric mixer, beat egg mixture until cool and thick, about 5 minutes.
Beat cream, liqueur and vanilla in another large bowl until stiff peaks form. Fold cream mixture into egg mixture.

Homemade Caramel Sauce (caramel recipe courtesy of Giver's Log)
Tools/Equipment:
3-4 quart saucepan
candy thermometer

Ingredients:
1 cup unsalted butter (2 sticks)
2 1/4 cups brown sugar
1 cup light corn syrup
1 14-oz can sweetened condensed milk
1 tsp vanilla extract

Cut butter into evenly sized cubes and melt over low heat in large 3-4 quart saucepan.
Once butter is fully melted, add brown sugar, being careful to avoid the sides of the pan. If any stray sugar crystals fall onto side of pan, carefully brush off with a wet pastry brush.
Once butter and sugar are fully combined, add corn syrup and condensed milk. Clip on candy thermometer to side of pan.
Cook mixture on low heat (still continually stirring) for about a minute or two. Increase heat to medium and continue to cook/ stir until mixture reaches 225 degrees. Once the mixture is removed from heat, stir in vanilla extract.

NOTE: If caramel is too thick, simply reheat and add in some heavy cream until combined.

Swiss Meringue Buttercream:
1 cup sugar
4 egg whites
3 sticks unsalted butter (at room temperature)
1 tbsp vanilla extract

Heat sugar, egg whites, and salt in a heatproof mixer bowl set over a pan of simmering water, whisking until sugar dissolves and mixture registers 160 degrees on a candy thermometer.

Return bowl to mixer, and whisk, gradually increasing speed from low to medium-high, until stiff, glossy peaks form, about 10 minutes. Reduce speed to medium. Add butter, a few pieces at a time, whisking well after each addition. Whisk in vanilla. Switch to a paddle attachment and beat until air bubbles are gone, 2 to 3 minutes more.

To assemble the cupcakes:

Once cupcakes are cool, core out the center of each one. Using a pastry bag, pipe a small amount of caramel sauce, then pipe coffee mousse until the center is almost full, and then top with another piping of caramel. Once all cupcakes are filled, pipe swiss meringue buttercream onto each one using a pastry bag fitted with a large star tip. Lastly, use a sturdy plastic freezer bag or disposable plastic pastry bag with a small hole cut out of it and drizzle caramel on top of each cupcake.