Three-Layer Chocolate Ganache Cake

Directions

1. Preheat oven to 350°. Line bottoms of 3 greased 9-in. round baking pans with parchment; grease paper. In a large bowl, whisk flour, sugar, cocoa and baking soda. Beat in mayonnaise, coffee and vanilla. Transfer batter to prepared pans. Bake until a toothpick inserted in center comes out clean, 30-35 minutes. Cool in pans 10 minutes before removing to wire racks; remove paper. Cool completely.
2. For filling, in a small heavy saucepan, mix sugar and cornstarch. Whisk in milk. Cook and stir over medium heat until thickened and bubbly. Reduce heat to low; cook and stir 2 minutes longer. Remove from heat; stir in vanilla. Cool completely. In a large bowl, cream butter. Gradually beat in cooled mixture. Stir in chocolate chips.
3. For ganache, place chocolate in a large bowl. In a small saucepan, bring cream just to a boil. Pour over chocolate; let stand 5 minutes. Stir with a whisk until smooth. Stir in vanilla. Cool to room temperature, stirring occasionally. Refrigerate, covered, until cold. Beat ganache just until soft peaks form, 15-30 seconds (do not overbeat).
4. Place 1 cake layer on a serving plate; spread with half of the filling. Repeat layers. Top with remaining cake layer. Frost top and side of cake with ganache. In a microwave-safe bowl, combine chocolate, cream and butter. Microwave at 50% power until smooth, 1-2 minutes, stirring twice. Cool slightly, stirring occasionally. Drizzle over cake, allowing some to flow over side. Refrigerate at least 2 hours before serving.