• Preheat Oven to 350F.
• Grease and line a 4-inch round baking pan with parchment paper and set aside. If using a silicone mold.
• Add all the wet ingredients except the milk (half-whisked egg, oil, sour cream, vanilla extract, sugar) in a medium-sized bowl. Mix it all in until it comes together. Add in the flour, salt, baking powder, and baking soda. Whisk all the ingredients together just until the wet combines with the dry.
• In a microwave-safe cup heat the milk until it's hot and then add it to the cake batter. Scrape the sides of the bowl and mix until all the ingredients combine. Bake the cake batter in the prepared pan.
• Bake the mini cakes for 8 to 10 minutes checking the sides and top of the cake for doneness.
• Allow the cakes to fully cool and make the buttercream.
• In a large size bowl add in the butter and cream on high for 4 minutes. Add in the vanilla and powdered sugar and continue to beat for another 2 to 3 minutes on high.

Cake Assembly and Decorating

• Once the cake layers have cooled assemble the cake for decorating.
• Cut out an 8x8in parchment paper and place it on your decorating stand. Place one of the layers in the middle of the parchment paper.
• With an offset spatula or spatula of choice spread some buttercream in the middle of the layers. If a filling is desired, fill a piping bag with buttercream and then pipe a border of buttercream on the inner edges of the cake and then fill and spread the filling, and then place the next layer on top. Repeat this step if a 3rd layer is desired.
• Apply a thin layer of buttercream outside of the cake to create the crumb coat. Set the cake in the fridge for at least 20 minutes or until the outside of the buttercream is firm to the touch. Frost the outside of the cake and then use a bench scraper to straighten the sides. Pipe and decorate the cake as desired.