Heat milk and chocolate until melted and combined, cool to room temperature.*
Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter and sugar on med-high until pale and fluffy (approx 3mins). Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and milk mixture, beginning and ending with flour (4 additions of flour and 3 of milk). Fully incorporating after each addition.
Bake for about 40mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack and cool completely.
White Chocolate Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.**
Place bowl over a pot with 1-2" of simmering water and stir constantly with a whisk until the mixture is hot and no longer grainy to the touch or reads 160F on a candy thermometer (approx. 3mins)
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.***
Add melted, cooled white chocolate and whip until smooth.
White Chocolate Ganache:
Place chopped chocolate and cream in a microwave safe bowl. Microwave in 5-10 second increments, stirring in between, until smooth and combined. Add a few drops of bright white color gel to get the desired color. Set aside to thicken and cool completely.
Place one layer of cake on a cake stand or serving plate. Top with 1 cup of buttercream and spread evenly. Repeat with remaining layers and crumb coat the cake. Chill for 20mins.
Frost and smooth the sides with the remaining frosting. Use a scalloped cake comb to create the textured effect on the sides. Smooth the top. Chill for 30mins until frosting is cold and firm.
Using a small spoon, place dollops of ganache around the top edges of the chilled cake, allowing some to drip down. Fill in the top of the cake with more ganache and spread evenly with an offset spatula. Chill to set ganache (5 mins).
Pipe dollops on top using an Ateco or Wilton 1M tip, top each with a Lindt White Chocolate Truffle if desired. Sprinkle chocolate shavings along the bottom and to fill in the top.
* You can do this in the microwave, stirring between 30 second bursts or in a pot in the stove, stirring constantly, or in a double boiler, stirring occasionally. ** Wipe your mixer bowl and whisk down with lemon juice or vinegar to make sure it is completely grease free and make sure there is no trace of yolk in your whites or your meringue will not stiffen. *** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth. If it looks soupy, place it in the fridge for 20mins and rewhip.