Rich Double Chocolate Cake - bittersweet chocolate

Method

• Cake: Coat two 9 x 2-inch round baking pans with nonstick cooking spray.
• Line bottoms with waxed paper; spray paper.
• Break up chocolate into a small microwave-safe bowl; add oil.
• Microwave on HIGH power for 1 minute; stir until smooth.
• If needed, heat an additional 15 seconds.
• Cool slightly.
• In medium-size bowl, mix flour, cocoa, baking soda and salt.
• In large bowl, with mixer on medium speed, beat butter and sugar until fluffy, about 3 minutes.
• Add eggs, one at a time, beating after each.
• Beat in chocolate mixture and vanilla.
• Place vinegar in a 2-cup capacity measuring cup.
• Add milk and stir until blended.
• On low speed, beat flour mixture into butter mixture, alternating with milk, beginning and ending with flour; beat 1 minute.
• Spread into pans.
• Bake at 350F for 35 minutes or until toothpick inserted in centers tests clean.
• Cool cakes in pans on wire racks 15 minutes.
• Turn cakes out onto racks; cool layers completely (about 2 hours).
• Prepare Frosting: In large glass bowl, microwave white chocolate on 50% power for 1 minute; stir.
• Microwave another 30 seconds until melted and smooth.
• Let cool slightly.
• With mixer, beat in sour cream and butter until smooth.
• Refrigerate 10 minutes.
• On low speed, beat in sugar until blended; continue to beat until fluffy.
• If too soft, refrigerate 10 minutes.
• Spread 1 cup frosting on top of one layer.
• Stack with second cake layer.
• Spread thin coating of frosting around side of cake.
• Refrigerate or freeze 15 minutes, until firm.
• Frost side and top with remaining frosting; garnish with curls, if desired.
• Refrigerate until set, 20 minutes.