Preheat oven to 350°F. Line 2 9-inch round cake pans with parchment and spray with nonstick spray. Set aside.
In a small mixing bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
3 cups cake flour, 2½ teaspoons baking powder, ¾ teaspoon baking soda, ½ teaspoon kosher salt
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed for 1 minute. Add in the eggs and beat for another minute. Add in the buttermilk, sour cream, and vanilla and mix to bring together.
2 cups granulated sugar, 1¼ cups unsalted butter, 4 large eggs, 1 cup buttermilk, ¼ cup sour cream, 1 tablespoon pure vanilla extract
Add the flour mixture to the wet ingredients and stir just to combine. Fold in the chocolate chips.
1½ cups mini chocolate chips
Divide the batter evenly between the 2 cake pans and place them into the oven to bake. Bake for 35 minutes, or until a toothpick inserted comes out clean or with moist crumbs. Once baked, remove from the oven and place onto a cooling rack.
While the cakes are cooling, make the frosting. Place the butter, sweetened condensed milk, and salt into the bowl of a stand mixer fitted with a whisk attachment. Whip on high for 3 minutes, or until the mixture is fluffy. Add in the powdered sugar and vanilla and whip for another 1-2 minutes. Fill a piping bag fitted with a tip with ½ cup of frosting.
2 cups unsalted butter, 14 ounces sweetened condensed milk, ¾ teaspoon kosher salt, 2¼ cups powdered sugar, 1 teaspoon pure vanilla extract
To make the chocolate ganache, warm the heavy cream in the microwave for 45-60 seconds. Pour the heated heavy cream over the chocolate chips and let set for 30 seconds to allow the chocolate chips to begin to melt. Whisk together until a smooth ganache has formed. Let the ganache set and cool while you frost the cake.
½ cup heavy cream, ¾ cup chocolate chips
Place the first cake layer onto a plate or cake stand. Spread ⅓ cup of frosting onto the bottom layer. Place the second layer on top of the bottom layer. Frost the top of the cake first and then the sides. To smooth the sides of the cake, hold an offset spatula parallel to the cake at a 45-degree angle and pull the frosting around the cake, filling in any holes as you go. It may take several turns around the cake to get it as smooth as you would like. Once the sides are smoothed, there should be a sort of frosting wall around the top edge of the cake. Pull the offset spatula towards the center, in a circle, smoothing the wall and creating a smooth edge around the cake.
Once the cake is frosted, pour the ganache on top and spread it to the edges of the cake and allow it to drip down the sides. Pipe little swirls of frosting in a ring formation around the edge of the cake on top of the ganache. If you so desire, sprinkle some mini chocolate chips on top of the frosting swirls.