Preheat the oven to 350 degrees F. Grease two 9- by 2-inch round cake pans, attach a parchment circle to the bottom of each pan, grease and flour again.
Mix well the flour, baking powder, salt, baking soda, cinnamon, ginger, nutmeg and cayenne in a bowl. Toss in the walnuts and raisins to coat.
Using a stand mixer, whisk the sugar, oil, vanilla and eggs for 3 minutes on medium speed. Add the carrots and mix well. Add the dry ingredients and mix for 1 minute on low speed to incorporate.
Divide the batter between the prepared pans. They will be about two-thirds full.
Bake until a toothpick inserted in center comes out clean, 50 to 60 minutes.
Allow the cake to cool for 10 to 15 minutes, and then remove the cake from the pans onto a cooling rack. Cool completely before applying the frosting.
To frost the cake, take the cooled cakes and carefully slice each one horizontally with a serrated knife to create 4 layers of cake. Place a small dollop of the Ron's White Chocolate Buttercream in the center of the serving platter; this will help affix your cake to the platter. Then, put the first layer of cake on the platter. Apply a generous amount of buttercream to the top center of the cake. Using a flat spatula, spread the buttercream, starting at the center and moving outward to the sides of the cake. It's important to use enough buttercream and to let the spatula only touch the top of it, so you don't pick up any crumbs from the cake.
Next, fit the second layer on top and repeat. Then, refrigerate for 5 to 10 minutes to harden the fillings/buttercream.
Repeat with the third layer and refrigerate for an additional 5 to 10 minutes.
Lastly, add the fourth layer and apply buttercream until evenly distributed on both the top and sides of the cake.
This makes a very tall cake. To serve, cut into strips the length of the cake and 2 inches wide and 1-inch thick rectangular cake slices.
Place the sugar and egg whites in large metal mixer bowl set over simmering water. Whisk constantly until the sugar melts and the mixture is very thin and warm.
Remove the bowl from the heat and whisk on high speed until stiff peaks form, about 5 minutes.
Continue beating on low speed until cool, about 15 more minutes.
Beat in small pieces of the cool but soft butter on low speed. The mixture may curdle before coming together. Gradually beat in the melted and cooled white chocolate.
Re-beat occasionally while frosting the cake to maintain a smooth texture.
Use moistened magic cake strips around each pan for level rising and baking. Tips of the trade: Make sure the bottom of the mixer bowl does not touch simmering water. Your egg whites may become a sweet scrambled breakfast dish! Finished buttercream may be kept covered and refrigerated for a week. Professional chefs prefer to use pasteurized egg whites - no need to separate fresh eggs, no wasted yolks and safer all around. Buttercream also freezes well for up to 6 months. Chilled buttercream must be brought to room temperature before beating, otherwise it will curdle. If such a disaster strikes, do not panic! Keep beating over simmering water and eventually the mixture will come together again.