For the cake:
2 oz. bittersweet or semisweet chocolate, chopped
2 oz. unsweetened chocolate, chopped
6 tbsp. water
4 large eggs, separated
16 tbsp. unsalted butter, at room temperature
1½ cups sugar, divided
2 cups all-purpose flour
1 tsp. baking powder
1 tsp. baking soda
½ tsp. salt
1 cup buttermilk, at room temperature
1 tsp. vanilla extract
For the rum syrup:
1 cup water
¾ cup sugar
2 tbsp. dark rum
For the filling:
1 cup heavy cream
1 cup sugar
3 large egg yolks
6 tbsp. butter, cut into small pieces
½ tsp. salt
1 cup pecans, toasted and finely chopped
1 1/3 cups unsweetened coconut, toasted*
*I was unable to find unsweetened coconut, so I used sweetened and the filling tasted great
For the icing:
8 oz. bittersweet or semisweet chocolate, chopped
2 tbsp. light corn syrup
3 tbsp. unsalted butter
1 cup heavy cream
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To make the cake, preheat the oven to 350° F. Line two 9-inch round cake pans with parchment paper. Butter and flour the sides of the pans; set aside.
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Using a double boiler (or the microwave in short bursts), melt the bittersweet and unsweetened chocolate with the water, stirring until smooth. Set aside until the mixture cools to room temperature.
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In the clean, dry bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on high speed until they form soft droopy peaks. Slowly add ¼ cup of the sugar and continue beating until stiff peaks form. Transfer the egg whites to a separate bowl and return the mixer bowl to the mixer base.
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In the bowl the electric mixer fitted with the paddle attachment, combine the butter with 1¼ cups of the sugar. Beat on medium-high speed until light and fluffy, about 5 minutes. Beat in the melted chocolate. Mix in the egg yolks one at a time, scraping down the bowl as needed.
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In another bowl, sift together the flour, baking powder, baking soda and salt. Mix half of the dry ingredients into the butter mixture on low speed just until incorporated. Mix in the buttermilk and vanilla extract until combined. Mix in the remaining dry ingredients just until incorporated. Using a rubber spatula, gently fold about a third of the egg whites into the batter to lighten it. Then fold in the remaining egg whites just until incorporated.
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Divide the batter between the prepared cake pans and bake in the preheated oven for about 45 minutes, until a toothpick inserted in the center comes out clean. Allow to cool in the cake pans for 10 minutes, then remove from the pans and transfer to a wire rack to cool completely.
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While the cakes are cooling, make the rum syrup. Combine the water and sugar in a small saucepan over medium-high heat and heat until the sugar is dissolved, stirring occasionally. Off the heat, stir in the rum.
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To make the filling, combine the cream, sugar and egg yolks in a medium saucepan. Put the butter, pecans and coconut in a mixing bowl; set aside. Heat the cream mixture and cook, stirring constantly and scraping the bottom until the mixture begins to thicken and coats the back of a spoon (170-175° F.) Pour the hot custard immediately into the pecan coconut mixture and stir until the butter is melted. Cool completely to room temperature. The mixture will thicken as it cools.
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(*Note – I found that my filling was still a bit thin even after cooling. I mixed in more coconut and that thickened it up perfectly. Probably depends on how tightly packed the coconut is in measuring.)
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To make the icing, place the chopped chocolate in a bowl with the corn syrup and butter. Heat the cream just until it begins to boil. Remove from the heat and pour over the chocolate. Let stand for 1 minute, then stir until smooth. Chill thoroughly in the refrigerator or freezer until firm enough for decorating.
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To assemble the cake, cut the two cake layers in half horizontally to yield four layers. Set the first layer on a cake circle, cut side up. Brush well with the rum syrup. Spread ¾ cup of the coconut filling over the cake layer, making sure to reach the edges. Set another cake layer on top of the filling. Repeat, using the syrup to brush each cake layer, then spreading ¾ cup of the coconut filling over each layer, including the top. Ice the sides of the cake with the chilled chocolate icing. Pipe a decorative border around the top layer, encircling the coconut topping.