Sift cake flour, cocoa, baking soda, and salt into medium bowl. Using an electric mixer, beat butter in large bowl until smooth. Add brown sugar and beat until well blended, about 2 minutes. Add eggs 1 at a time, beating well after each addition. Mix in vanilla. Add flour mixture in 3 additions alternately with buttermilk in 2 additions, beating just until blended after each addition
Position rack in center of oven; preheat to 325° F. Generously butter two 9-inch cake pans with 2-inch-high sides; dust with flour, tapping out any excess.
Divide batter between pans; smooth tops. Bake cakes until tester inserted into center comes out clean, about 40 minutes. Cool cakes in pans on cooling rack for 15 minutes. Run small knife around sides of pans to loosen cakes. Invert cakes onto racks; lift pans off cakes. Cool completely.
1/3 cup natural unsweetened cocoa powder
1 ½ cups chilled heavy whipping cream, divided
1 1/3 cups sugar
16 ounces of cream cheese
Sift cocoa powder into large bowl. Bring 1 cup cream to boil in small saucepan. Slowly pour cream over cocoa, whisking until cocoa is completely dissolved, about 1 minute. Add ½ cup cream and sugar; stir until sugar dissolves. Chill until cold, at least 2 hours. Can be made 1 day ahead. Cover; keep chilled.
Add cream cheese to cocoa mixture. Using electric mixer, beat on low speed until blended and smooth. Increase speed to medium-high; beat until mixture is thick and medium-firm peaks form when beaters are lifted, about 2 minutes.
Using pastry brush, brush off crumbs from cakes. Place 1 cake layer, top side up, on platter. Frost first layer, add a layer of sliced strawberries if desired, then cover with more frosting. Add second layer of cake and finish frosting. Garnish with sliced strawberries.