• Preheat the oven to 350 degrees.  Line the bottom of three 8-inch round cake pans with parchment paper and spray the sides with non-stick spray.
• For each flavor of cake, mix the ingredients in a large mixing bowl with the cake mix, eggs, milk, oil and sour cream.  (Leave sour cream out of the strawberry cake.)  Beat with a hand mixer for 2-3 minutes until batter is fluffy and smooth.
• Place 2 1/2 cups of batter into one of the prepared cake pans.  Use the remaining batter for another purpose.
• Bake cake for 24-30 minutes, depending on your oven, or until a toothpick inserted in the center comes out clean.
• Remove cakes and cool for 10 minutes.  Carefully remove cakes from the pans to cooling racks and cool completely.
• Wrap each cake layer in plastic wrap and place in the freezer to firm up for 2 or more hours if time allows.  This makes it easier to assemble and frost the cake.

For Buttercream Frosting:

• In stand mixer cream butter and powdered sugar together and beat until fluffy.
• Gradually add in milk and mix until light and fluffy, then mix in vanilla and a pinch of salt.
• For chocolate frosting remove 1 cup frosting to a mixing bowl.  Add 3 oz melted and cooled semi-sweet chocolate and mix until blended.  Save the rest of the melted chocolate to drizzle over the top of the cake.
• For vanilla frosting layer use 1 cup plain buttercream frosting.
• For strawberry layer use remaining frosting and add 2 tsp strawberry flavoring and 2 drops red food coloring.  Mix until blended.

Assembly of cake:

• Trim the top of each cake layer so the surface is flat and even.
• Place the chocolate cake layer top-side up onto the serving plate. Mound chocolate frosting onto the cake layer and spread smoothly with an offset spatula or knife to the edges.
• Place the vanilla layer of cake top-side down on top of the chocolate frosted layer.  Press down gently to seal the layers together. Spread 1 cup vanilla frosting over the vanilla cake layer and spread smoothly with an offset spatula or knife to the edges.
• Place strawberry cake layer on top-side down and press down to seal the layers together.  Spread a thin layer of strawberry frosting over the top and down the sides of the cake to seal in all of the crumbs and smooth the sides between the layers.  Freeze for 15-30 minutes.
• Mound the remaining frosting over the top and down the sides of the cake and use an offset spatula to spread the frosting evenly.  If desired you can transfer some frosting to a piping bag and pipe a border around the top and bottom perimeter of the cake. Refrigerate any leftover frosting and use for other purpose.
• Drizzle remaining melted chocolate over the top of the cake and top with fanned sliced strawberries if desired.

• Notes:

  *Store in an airtight cake container or cover loosely to keep cake from drying out. *Refrigerate for up to 3-4 days for best texture and flavor.  Let come to room temperature to serve. *You can make unfrosted cakes ahead of time and freeze them until ready to use.