Ganache-Filled Chocolate Cupcakes with Seven-Minute Meringe Frosting

Preparation

1. For cupcakes:

   Step 1

   Preheat oven to 350°F. Line two 12-cup standard muffin pans with paper liners. Sift flour, cocoa powder, baking soda, and salt into medium bowl. Using electric mixer, beat sugar and butter in large bowl until light and fluffy, about 2 minutes. Add eggs 1 at a time, beating until well incorporated after each addition. Beat in vanilla, half of flour mixture, then 1 cup hot water. Add remaining flour mixture; beat just until blended. Let batter stand until cooled and slightly thickened, about 5 minutes. Stir in chocolate chips. Divide batter among muffin papers (about 1/4 cup batter each).

   Step 2

   Bake cupcakes until tester inserted into center comes out with some crumbs attached, 22 to 25 minutes. Cool cupcakes completely in pans.

2. For filling and frosting:

   Step 3

   Bring cream just to boil in heavy small saucepan. Place chocolate chips in medium bowl; pour hot cream over. Let stand 1 minute, then whisk until melted and smooth. Let stand at room temperature until cool and firm, about 2 hours. (Alternatively, chill ganache until cool and firm, stirring occasionally, about 1 hour.) DO AHEAD: Can be made 4 hours ahead. Let stand at room temperature.

   Step 4

   Whisk 1/3 cup water, sugar, egg whites, cream of tartar, and coarse salt to blend in large metal bowl. Set bowl over saucepan of barely simmering water. Using electric mixer, beat mixture until soft peaks form, about 5 minutes. Remove bowl from over water and continue beating until frosting is cool to touch, stiff, and billowy, about 2 minutes. Beat vanilla into frosting.

   Step 5

   Using thumb, press down center of each cupcake from top to bottom, forming deep pocket. Spoon or pipe ganache into pocket of each cupcake.

   Step 6

   Frost cupcakes, forming tall peaks. DO AHEAD: Cupcakes can be made 1 day ahead. Cover with cake dome and store at room temperature.