- 2 tablespoons light corn syrup
- 1/2 cup heavy whipping cream
- 1/4 cup (1/2 stick) unsalted butter, diced
- 1/4 cup crème fraîche or sour cream
- 1/2 teaspoon fresh lemon juice
- Large pinch of fine fleur de sel* plus additional for assembly
GANACHE FILLING AND FROSTING
- 1 1/2 pounds bittersweet chocolate, chopped
- 3 cups heavy whipping cream
- 1 3/4 cups all purpose flour
- 3/4 cup unsweetened cocoa powder
- 1 1/2 teaspoons baking powder
- 1 1/2 teaspoons baking soda
- 1/2 cup (1 stick) unsalted butter, melted
- 1 tablespoon instant espresso powder or instant coffee
- 1 1/4 cups almonds, toasted, coarsely chopped
Stir sugar, 1/4 cup water, and corn syrup in deep medium saucepan over low heat until sugar dissolves. Increase heat to medium; cover pan and cook 4 minutes. Uncover; increase heat to high. Boil without stirring until syrup is deep amber, occasionally brushing down pan sides with wet pastry brush, about 6 minutes. Remove from heat. Add cream (mixture will bubble). Whisk in butter, then crème fraîche, lemon juice, and pinch of fleur de sel. Cool completely. DO AHEAD Can be made 3 days ahead. Cover and chill. Bring to room temperature before using.
GANACHE FILLING AND FROSTING
Place chocolate in large bowl. Bring cream to simmer in medium saucepan. Pour cream over chocolate; let soften 1 minute. Whisk until chocolate is smooth. Cool, then cover and chill overnight. DO AHEAD Ganache can be made 3 days ahead. Keep chilled. Bring to room temperature before using.
Position rack in center of oven and preheat to 350°F. Butter two 9-inch-diameter cake pans with 2-inch-high sides. Line bottom of each with parchment paper; butter paper and dust pan with flour.
Sift sugar, flour, cocoa powder, baking powder, baking soda, and salt into large bowl. Add milk, eggs, and melted butter. Using electric mixer, beat at low speed until blended. Increase speed and beat 2 minutes. Stir 1 cup hot water and espresso powder in small bowl to dissolve. Add to batter; beat until blended (batter will be thin). Divide batter between pans (about 3 cups each).
Bake cakes until tester inserted into center comes out clean, about 32 minutes. Cool cakes in pans on racks 10 minutes. Cut around cakes; turn out onto racks. Peel off parchment and cool completely.
Using long serrated knife, cut each cake horizontally in half. Place 1 layer on platter; spread with 1/2 cup room-temperature ganache. Spoon 3/4 cup ganache into pastry bag fitted with 1/4-inch plain round tip. Pipe ring of ganache around edge of layer. Spread 1/4 cup room-temperature caramel filling evenly inside ring. Sprinkle caramel with large pinch of fleur de sel, then 1 tablespoon almonds. Top with second cake layer, ganache, ganache ring, caramel filling, fleur de sel, and almonds. Repeat with third cake layer. Top with fourth cake layer, cut side down. Spread remaining ganache over top and sides of cake. Press remaining almonds onto sides. DO AHEAD Can be made 2 days ahead. Cover with cake dome and chill. Let cake stand at room temperature 1 hour.
*A type of sea salt; available at some supermarkets and at specialty foods stores.