Step 1

Preheat oven to 350°F. Stir together chopped chocolate and hot coffee in a medium microwavable bowl. Microwave on HIGH until melted and smooth, 30 seconds to 1 minute, stirring mixture after 30 seconds. Set aside.

Step 2

Whisk together flour, baking soda, and salt in a medium bowl. Beat butter and sugars with a heavy-duty stand mixer on medium speed until light and fluffy, about 3 minutes. Add yolks, 1 at a time, beating just until blended after each addition. Add melted chocolate mixture and vanilla, and beat on low speed until blended. Add flour mixture alternately with buttermilk, beginning and ending with flour mixture. Beat on low speed just until blended after each addition.

Step 3

Place egg whites in a separate clean bowl, and beat with an electric mixer on high speed until stiff peaks form, about 3 minutes. Gently fold into batter. Divide batter among 3 9-inch round cake pans lined with parchment paper.

Step 4

Bake in preheated oven until a wooden pick inserted in center comes out clean, 24 to 28 minutes. Remove pans from oven; gently run a knife around outer edge of cake layers to loosen from sides of pans. Cool in pans on wire racks 15 minutes. Remove from pans; transfer to wire racks. Discard parchment paper. Cool completely, about 1 hour. Press slightly warm Coconut-Pecan Frosting between layers and on top and sides of cake. Let stand until frosting is completely cool and set, about 15 minutes.