Step 1

Preheat oven to 350°F. Line three eight-inch pans with parchment rounds, and grease with non-stick baking spray.

Step 2

Mix together all dry ingredients (flour, baking powder, sugar, and salt) in a stand mixer with a paddle until fully combined.

Step 3

Mix chunks of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.

Step 4

Pour in egg whites, and mix on low until just incorporated. Mix in the buttermilk in two installments, on a low speed.

Step 5

Add in vanilla and oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on low speed for about 15 seconds.

Step 6

Mix the batter on a low speed, scraping the sides and bottom of the bowl part way through to evenly color the batter.

Step 7

Divide batter evenly between the prepared cake pans.

Step 8

Bake for 34-36 minutes (or until a skewer comes out clean).

Step 9

Allow to cool for 10 minutes, then run a small offset spatula around perimeter of the pan to separate the cake from the pan.

Step 10

Place cake layers into the freezer for 45 minutes, to accelerate the cooling process.

Step 11

Beat the butter on a medium speed for 30 seconds with a paddle attachment or hand mixer until smooth.

Step 12

Mix in the vanilla extract and salt on a low speed.

Step 13

Slowly add in the powdered sugar, 1 cup at a time. Alternate with small splashes of cream.

Step 14

Mix on low for a couple extra minutes, to make the frosting super smooth.

Step 15

If the frosting is too thick, add in additional cream (1 teaspoon at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).

Step 16

Heat heavy cream in a heat proof bowl in the microwave for 45 seconds, until it's just beginning to bubble.

Step 17

Gently pour white chocolate chips into the heavy cream, making sure they are fully covered with cream. Allow mixture to sit for 1 minute.

Step 18

Stir slowly until the cream and white chocolate are combined. Some bits of chocolate may not be fully melted yet. Heat the mixture again for 20 seconds, and stir. Repeat as necessary until all the chocolate bits are fully melted and incorporated.

Step 19

Add in gel food coloring, if desired. Allow to cool until desired viscosity is reached (barely warm to the touch).

Step 20

If it seems too thin or thick, you can add a touch more chocolate chips or heavy cream! The type of cream and white chocolate that you use can affect the consistency, so feel free to adjust as needed.

Step 21

Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.

Step 22

Add an even layer of buttercream between each cake layer with a large offset spatula.

Step 23

Spread a thin coat of frosting around the the cake, to fully cover the cake layers.

Step 24

Smooth using a bench scraper, then chill the cake in the fridge (20 minutes) or freezer (10 minutes) until the frosting is firm to the touch.

Step 25

Add a second, thicker layer of frosting to the cake, and smooth using a bench scraper.

Step 26

Chill the cake again in the fridge (20 minutes) or freezer (10 minutes) until the frosting is firm to the touch.

Step 27

Add the drips to the cake using a plastic squirt bottle.

Step 28

Then decorate as desired!