Chocolate Cake with Fleur de Sel Caramel Filling
Adapted from Bon Appétit
Serves 12-14

The original recipe called for a light sprinkling of chopped almonds in between each layer and on the outside of the cake.  Because neither Lauren or I like nuts in our desserts, I opted to leave them out.  If you wish to include them, you will need 1 1/4 cups chopped almonds total.  Each layer gets sprinkled with 1 tablespoon, the rest goes onto the sides of the frosted cake.

Caramel Filling
1 cup sugar
1/4 cup water
2 tbsp. light corn syrup
1/2 cup heavy whipping cream
1/4 cup (1/2 stick) unsalted butter, diced
1/4 cup crème fraiche or sour cream
1/2 tsp. 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

Cake
2 cups sugar
1 3/4 cups flour
3/4 cup unsweetened cocoa powder
1 1/2 tsp. baking powder
1 1/2 tsp. baking soda
1 tsp. salt
1 cup whole milk
2 large eggs
1/2 cup (1 stick) unsalted butter, melted
1 cup hot water
1 tbsp. instant espresso powder or instant coffee

Caramel Filling: 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 fraiche, lemon juice, and pinch of fleur de sel.  Cool completely.  (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.  (Can be made 3 days ahead.  Keep chilled.  Bring to room temperature before using. DT: Bringing it to room temperature is essential and it can take several hours.  Be sure to plan for that.)

Cake: 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.  (DT: The piped ring of ganache will keep help in keeping the caramel from oozing out the sides.) Top with second cake layer, ganache, ganache ring, caramel filling, and fleur de sel.  Repeat with third layer.  Top with fourth cake leyer, cut side down.  (DT: Put cake in freezer for 45 minutes to firm everything up and make frosting the cake easier.)  Spread remaining ganache over top and sides of cake.  (Can be made 2 days ahead.  Cover with cake dome and chill.  Let cake stand at room temperature 1 hour before serving.)