Preheat oven to 180°C/160°C fan-forced. Grease a 7cm-deep, 15cm (base) round cake pan, 7cm-deep, 20cm (base) round cake pan and 7cm-deep, 25cm (base) round cake pan. Line bases and sides of pans with baking paper.
Make 2 packet cakes following packet directions or homemade cakes (see related recipe). Spread batter into prepared 15cm pan until two-thirds full. Spread remaining batter into prepared 20cm pan. Bake 15cm pan for 30 to 35 minutes or until cooked through. Bake 20cm pan for 40 to 50 minutes or until cooked through. Stand in pans for 5 minutes. Turn out onto wire racks to cool completely. Make remaining cakes. Spread batter into prepared 25cm pan. Bake for 1 hour 15 minutes or until cooked through. Stand in pan for 10 minutes. Turn out onto a wire rack to cool completely.
Make icing: Using an electric mixer, beat butter in a bowl until light and fluffy. Gradually add half the sugar, beating to combine. Gradually add chocolate and remaining sugar, beating to combine. Gradually add milk, beating to combine.
Using a serrated knife, level tops of cakes. Cut 25cm cake horizontally into thirds. Place cake base on 30cm separator plate. Spread with 1 1/2 cups icing. Top with middle layer and 1 1/2 cups icing. Sandwich with cake top. Spread with 1 1/2 cups icing.
Repeat with 20cm cake and 25cm separator plate, using 3/4 cup icing for each layer.
Repeat with 15cm cake and 20cm separator plate, using 1/2 cup icing for each layer.
Position 4 pillars on large cake. Insert dowel through pillars into cake. Repeat with middle layer. Arrange raspberries on cakes. Secure middle cake on large layer. Secure small cake on middle layer. Serve.
