Salted Caramel Chocolate Cake

Method (cake)

Whisk together the dry ingredients. Add eggs, oil, and vanilla, beating until smooth. Gradually add water, beating until smooth. Pour batter into prepared pans. Bake cakes for 35-38 minutes (30 if you use a 9" pan), or until cake tester inserted into the center comes out clean. Cool cakes in pan for 15 minutes, then turn them out of the pans to cool completely on a rack.

Method (marshmallow filling)

Place 2 egg whites in large mixing bowl. Beat until egg whites are foamy and thick; they should mound in the bowl, without holding a peak. Set aside. Combine sugar, cream of tartar, water, and salt in a saucepan. Bring to boil, stirring frequently; the sugar should be dissolved. If sugar hasn't dissolved, cook and stir a bit more until it has. Begin to beat egg whites. Immediately pour boiling sugar syrup into egg whites in a slow stream, beating throughout. As you beat, mixture will thicken. Once syrup is added, stir in vanilla, and continue to beat until the frosting is thick and will hold a peak.

Method (milk chocolate mousse)

Melt chocolate over a double boiler. Bring water to a boil. Whisk boiling water into chocolate until completely mixed. Allow to cool slightly. Whip cream to soft peaks. Fold cream into chocolate mixture, pour into a container with lid and let set for at least 24 hours.

Method (buttercream)

Combine whites and salt in a very large bowl. Stir water and 1 1/3 cups sugar in a 3- to 4-quart heavy saucepan until sugar is dissolved, then bring to boil over moderate heat, without stirring, brushing any sugar crystals down side of pan with a pastry brush dipped in water. When syrup reaches a boil, start beating egg whites with an electric mixer at medium-high speed until frothy, then gradually add remaining 2 tablespoons sugar and beat at medium speed until whites just hold soft peaks. (Don't beat again until sugar syrup is ready.) Meanwhile, put thermometer into sugar syrup and continue boiling until syrup registers 238 to 242°F. Immediately remove from heat and, with mixer at high speed, slowly pour hot syrup in a thin stream down side of bowl into whites, beating constantly. Beat, scraping down side of bowl with a rubber spatula, until meringue is cool to the touch, about 10 minutes in a stand mixer or 15 with a handheld (meringue must be cooled before proceeding). With mixer on medium, gradually add butter 1 piece at a time, beating well after each addition until incorporated. (Buttercream will look soupy after some butter is added if meringue is still warm. If so, briefly chill bottom of bowl in a large bowl filled with ice water for a few seconds before continuing to beat in remaining butter.) Continue beating until buttercream is smooth. (Mixture may look curdled before all of butter is added but will come back together by the time beating is finished.) Add vanilla and beat 1 minute more.