Sour Cream Fudge Layer Cake with Chocolate Butter Icing

Cake:

Adjust oven rack to center position and heat oven to 350 degrees. Grease two 9-by-1 1/2-inch round baking pans with shortening. Line pan bottoms with waxed or parchment paper; grease paper as well. Dust pans with flour; tap out excess.

Mix cocoa and instant coffee in small bowl; add boiling water and mix until smooth. Cool to room temperature, then stir in vanilla and sour cream.

Beat butter in bowl of electric mixer set at medium-high speed until smooth and shiny, about 30 seconds. Gradually sprinkle in sugar; beat until mixture is fluffy and almost white, 3 to 5 minutes. Add eggs one at a time, beating 1 full minute after each addition.

Whisk flour, baking soda and salt in medium bowl. With mixer on lowest speed, add about 1/3 of dry ingredients to batter, followed immediately by about 1/3 of cocoa mixture; mix until ingredients are almost incorporated into batter. Repeat process twice more. When batter appears blended, stop mixer and scrape bowl sides with rubber spatula. Return mixer to low speed; beat until batter looks satiny, about 15 seconds longer.

Divide batter evenly between pans. With rubber spatula, run batter to pan sides and smooth top. Bake cakes until they feel firm in center when lightly pressed and a skewer comes out clean or with just a crumb or two adhering, 23 to 30 minutes. Transfer pans to wire racks; cool for 20 minutes. Run knife around perimeter of each pan, invert cakes onto racks, and peel off paper liners. Re-invert cakes onto additional racks; cool completely before frosting.

Icing:

Melt the chocolate and butter in a medium bowl set over pan of almost-simmering water. Stir in corn syrup. Set bowl of chocolate mixture over a larger bowl of ice water, stirring occasionally, until the frosting is just thick enough to spread. Apply icing onto first cake layer and spread with a long metal spatula, top with second cake layer, top second layer with icing, spread and then ice sides. Serve.