Preheat oven to 350°F. Grease and line three round 6-inch cake pans with parchment paper. Set aside.
Place all ingredients in a large bowl. With an electric mixer on low speed, mix until ingredients are just combined. Then turn mixer up to medium and beat for 2 minutes. Pour into prepared pans, dividing equally.
Bake for 40-45 minutes or until a toothpick inserted in middle of cake comes out clean. Let cool in pans.
For the buttercream
Beat softened butter on medium speed with an electric mixer. Beat for 3 minutes until smooth and creamy.
Add powdered sugar, salt, cream and vanilla extract with mixer running on low. Increase to high speed and beat for 3 minutes. Divide frosting evenly into two bowls. Color one bowl pink. Leave the other white. Cover with plastic wrap until ready to use. Frosting can stay at room temperature for 24 hours. After that, store in refrigerator for up to two weeks.
Filling, frosting and decorating the cake
Place first cake layer on a cake board or platter. Fill and frost the cake with a thin crumb coating of the white frosting. Refrigerate for an hour or overnight. Place remaining white frosting in a large pastry bag with ½" round pastry tip. Also place the pink frosting in a large pastry bag with ½" round pastry tip. Place cake board on a turntable and pipe a line of pink frosting around the base. Next pipe a white line of frosting just above the pink. Repeat until you get to the top. You should end with pink. Then frost the top with pink. Use a bench scraper to smooth the edges of the cake. Refrigerate for an hour or at least 30 minutes. Drizzle cake with chocolate mixture as directed below. Pipe pink dollops on top using a 1M pastry tip. Add sprinkles.
For the chocolate drizzle
Note: Do this step AFTER you have filled and frosted the cake.
In a medium sized microwave safe bowl, microwave the chocolate chips on high for 30 seconds. Stir. Heat for another 30 seconds. Stir until smooth, then stir in oil. Mix until completely combined. Place in a disposable pastry bag or zip-top baggie, twisting and secure with a twist tie. Cut off the pointed edge of the bag, so that you have a tiny hole to drizzle chocolate. It should be about the size of a #4 round pastry tip. Carefully drizzle chocolate mixture over the top edge of the cake, all the way around and then drizzle on top of the cake and spread with a butter knife or offset spatula.