• Preheat the oven to 350 degrees Fahrenheit. Cut out two parchment paper circles slightly smaller than the round 8-inch pans. Spray the bottom of the pans with nonstick cooking spray and place the parchment circles on the bottoms of the pans. Spray the insides of the pans as you normally would.
• In a medium sized bowl, combine the flour, baking powder, baking soda, and salt. Stir then set aside. In a small bowl, melt the dark chocolate chips and whole milk. Stir until smooth, then set aside to cool.
• In the bowl of a stand mixer, combine the oil, vanilla and both sugars. Mix for 1 minute on medium speed, then add the eggs one at a time beating well after each addition. Scrape the bowl with a spatula.
• Add the flour mixture to the egg mixture and start the mixer on low so it doesn't poof out of the bowl. Beat on medium until a smooth batter forms.
• While the mixer is on low speed, gradually add the buttermilk to the batter until it's completely combined, scraping the bowl with a spatula halfway through.
• Scoop 2 cups of the batter into a large bowl. Add the melted chocolate and stir to combine.
• Pour some vanilla batter into each cake pan and then pour the chocolate batter equally into both pans and then the rest of the vanilla batter to both pans. Use a knife to gently swirl the batters together in a figure eight motion.
• Bake the cakes until the tops are golden brown and a toothpick comes out clean around 35 to 37 minutes.
• Wait until the cakes are warm to remove from the pans. Wait until they are completely cool before frosting.

For the chocolate frosting:

• Melt ½ cup of dark chocolate chips and 1 tablespoon of milk in a small bowl in the microwave and stir then set aside.
• In the bowl of a stand mixer beat together the room temperature butter and 1 cup of powdered sugar for 1 minute on medium speed.
• Add 1 more cup of powdered sugar and 1 tablespoon of milk. Beat again for 1 minute on medium speed.
• Add 1 more cup of powdered sugar and 1 more tablespoon of milk and beat for 1 minute on medium speed.
• Add melted chocolate and 2 tablespoons of cocoa powder and mix for 30 more seconds.