Preheat oven to 170°C. Grease and line 20cm cake tins.
Cakes : Sift the flour, baking powder and salt into a large bowl. Combine milk and vanilla. Beat butter with a mixer on medium speed until smooth.
With the mixer running, gradually add Chelsea White Sugar and beat until the mixture turns pale and fluffy, about 3 minutes.
Reduce speed to low, and add the flour mixture in 3 additions, alternating with the milk. Begin and end with the flour mixture. Beat until just combined.
Beat the egg whites in a clean mixer bowl on medium speed until stiff peaks form, about 5 minutes. Gently fold the egg whites into the batter in 3 additions. Place 2 cups of batter in 6 separate bowls. Tint each bowl of batter with a little of the food color. Add food color a little at a time until the desired pastel tint is achieved. Fold the color in well with a rubber spatula until no streaks of white cake batter remains.
Spread the batter into the prepared pans and bake for 18 to 20 minutes.
Let the layers cool completely on a wire rack. Run a knife around the edges of the cakes and the pans before turning them out.
Level the tops of the cake with a serrated knife or a cake leveler. Save the cake scraps for ice cream topper.
Swiss Meringue Buttercream : In the bowl of an electric stand mixer, add the egg whites and Chelsea Icing Sugar. Whisk them together briefly by hand, just until they are combined so that the egg whites don't begin cooking by themselves. Fill a sauce pan with a few inches of water and bring to a simmer. Place the mixer bowl with the egg white mixture on top to create a double-boiler. The water should be kept at a simmer but should not touch the bottom of the bowl (the double-boiler acts as indirect heat for the egg white mixture).
Occasionally stirring, heat the egg white mixture until it reaches 68 to 71°C on a candy thermometer. The mixture should be very hot to the touch and the sugar should have dissolved.
Once the egg white mixture is hot, carefully return the bowl to the stand mixer. Fitted with the whisk attachment, beat the mixture on high speed for about 8 minutes. When done, the meringue should hold shiny, medium-stiff peaks and be cooled to room temperature.
Stop the mixer and swap out the whisk for the paddle attachment.
With the mixer on low, begin adding in the butter a couple tablespoons at a time. Use the paddle attachment to mix it in.
Once the butter has been mixed in, add the vanilla extract (you can add vanilla bean seeds if you have any).
Turn the mixer up to medium speed and mix until silky smooth. The cream should have a light and creamy texture and be free of most air bubbles.
Decoration : Mix the chocolate and butter together and melt to make the chocolate drip.
How to assemble: : Ice the cakes and layer on top of each other and put in fridge.
Once completely cooled, decorate with waffle cones, sprinkles and chocolate drip.