Coffee-Chocolate Layer Cake with Mocha-Mascarpone Frosting

Ingredients

• 1.5 teaspoons baking soda 
• 1 cup buttermilk 
• 2 cups cake flour 
• 0.3 cup natural cocoa powder unsweetened
• 3 large eggs 
• 2 cups brown sugar packed ()
• 1.5 cups heavy whipping cream chilled divided
• 1 tablespoon espresso powder instant
• 16 ounce mascarpone cheese chilled
• 0.8 teaspoon salt 
• 1.3 cups sugar 
• 0.8 cup butter unsalted room temperature ()
• 5.5 teaspoons vanilla extract 

Equipment

• bowl
• sauce pan
• baking paper
• oven
• knife
• blender
• hand mixer
• offset spatula
• pastry brush

Directions

1. Position rack in center of oven;preheat to 325°F. Generously butter two9-inch cake pans with 2-inch-high sides;dust with flour, tapping out any excess.Line bottom of pans with parchment paper.
2. Sift 2 cups cake flour, cocoa, bakingsoda, and salt into medium bowl. Usingelectric mixer, beat butter in large bowluntil smooth.
3. Add brown sugar and beatuntil well blended, about 2 minutes.
4. Addeggs 1 at a time, beating well after eachaddition.
5. Mix in vanilla.
6. Add flour mixturein 3 additions alternately with buttermilk in2 additions, beating just until blended aftereach addition. Gradually add hot espresso-watermixture, beating just until smooth.
7. Divide batter between pans; smoothtops.
8. Bake cakes until tester inserted intocenter comes out clean, about 40 minutes.Cool cakes in pans on rack 15 minutes. Runsmall knife around sides of pans to loosencakes. Invert cakes onto racks; lift pans offcakes and remove parchment.
9. Place wirerack atop each cake; invert again so topside is up. Cool completely. DO AHEAD: Canbe made 1 day ahead. Wrap each cake inplastic and store at room temperature.
10. Sift cocoa powder intolarge bowl; add espresso powder. Bring 1cup cream to boil in small saucepan. Slowlypour cream over cocoa mixture, whiskinguntil cocoa is completely dissolved, about1 minute.
11. Add 1/2 cup cream and sugar; stiruntil sugar dissolves. Chill until cold, atleast 2 hours. DO AHEAD: Can be made 1 dayahead. Cover; keep chilled.
12. Add mascarpone to chilled cocoamixture. Using electric mixer, beat on lowspeed until blended and smooth. Increasespeed to medium-high; beat until mixtureis thick and medium-firm peaks form whenbeaters are lifted, about 2 minutes (do notoverbeat or mixture will curdle).
13. Using pastry brush, brush off crumbsfrom cakes.
14. Place 1 cake layer, top side up,on platter. Spoon 13/4 cups frosting in dollopsover top of cake. Using offset spatula,spread frosting to edges. Top with secondcake layer, top side up, pressing to adhere.
15. Spread thin layer of frosting over top andsides of cake. Chill 10 minutes. Using offsetspatula, spread remaining frosting over topand sides of cake, swirling decoratively. Topwith chocolate curls, if desired. DO AHEAD: Can be made 1 day ahead. Cover with cakedome; chill.
16. Let stand at room temperature20 minutes before serving.
17. *An Italian cream cheese; sold at manysupermarkets and at Italian markets.