Cake: Heat oven to 350 degrees F. Coat three 9-inch round cake pans with nonstick cooking spray. Line bottoms with waxed paper; coat paper with spray.

Sift together flour, baking powder and salt into large bowl.

Beat butter in large bowl until smooth, 2 minutes. Add sugar; beat until light colored and fluffy, 5 minutes. Beat in eggs, one at a time, then beat for 1 minute.

Mix yogurt and milk in bowl. Beat flour mixture alternately with yogurt mixture into butter mixture, beginning and ending with flour mixture. Beat in vanilla. Divide batter into thirds, using 2 additional bowls. Leave one bowl as is. Stir melted chocolate and cocoa into second bowl. Tint the third bowl with food coloring.

Using large spoon, drop large dollops of the different batters, side by side, into pans. With tip of knife, broadly swirl batter to marble slightly.

Bake cake layers in 350 degree F oven for 25 to 30 minutes or until cakes spring back when lightly pressed in centers with fingertip. Let cakes cool in pans on wire racks 10 minutes. Invert cakes; remove pans and waxed paper. Let cakes cool completely on racks.

Frosting: Place finely chopped chocolate in medium-size bowl. Heat cream in saucepan just until simmering. Pour over chocolate. Let stand 5 minutes; whisk until smooth. Add liqueur, if using. Transfer to bowl; refrigerate until spreadable, 45 to 60 minutes.

Stack cake layers, spreading 1/3 cup frosting between layers. Using 2/3 cup frosting, spread very thin layer of frosting over sides and top of cake. Refrigerate 10 minutes to firm frosting slightly. Then loosely cover with plastic wrap; refrigerate until ready to proceed. Refrigerate rest of frosting.

About 45 minutes before serving, remove cake from refrigerator; unwrap plastic. Remelt frosting in top of double boiler over simmering water, until frosting reaches 80 degrees F. Pour a third over top of cake; spread with straight spatula, allowing frosting to dribble down sides. Repeat with remaining frosting, a third at a time. Smooth sides and tops. Refrigerate until firm, 20 minutes. Garnish with berries. Makes 16 servings.

Recipe can be prepared a day ahead through step 8. Or, whole cake can be assembled a day ahead. Before serving, let cake stand at room temperature to soften frosting slightly, 20 minutes.