1. Preheat the oven to 350 F and line 2 standard-sized muffin pans with 16 paper cupcake liners. Set aside. In a large mixing bowl, carefully sift together the flour, cocoa powder, baking powder, baking soda and salt. Whisk together.
2. In another medium sized bowl, whisk the eggs with the sugars, then whisk in the oil and vanilla. Add half of the wet ingredients to the dry ingredients and gently stir, then add half of the buttermilk, gently stirring again. Add the remaining wet ingredients, followed by the remaining buttermilk and stir until just combined.
3. Fill the cupcake liners only halfway full (this is important)! Filling the liners more than halfway full will cause the cupcakes to overflow out of the liners while they bake. Bake the cupcakes in the oven for 18-20 minutes or until a toothpick inserted in the center comes out clean. Remove the cupcakes and allow them to cool in their pans for 10 minutes before removing them to a wire rack.
4. While the cupcakes are baking, make the white chocolate ganache. Place the white chocolate in a heat-safe bowl, then warm the cream either on the stovetop or in the microwave until just before boiling (it should be very hot but not bubbling). Remove the cream from the heat, then pour it all over the white chocolate. Allow it all to sit, without stirring, for 3 minutes. Stir continuously until the ganache is completely smooth. Place the ganache in the fridge until you’re ready to use it.
5. Using a sharp paring knife, gently remove about a 1″ “plug” from the middle of each cupcake, reserving the removed cake (see blog post for pictures). Using a small spoon or piping bag, fill each hole with white chocolate ganache, about 2 teaspoons full. You will have some ganache left, to use for the buttercream. Replace the cake “plug” on top of the cupcake.
6. Prepare the buttercreams. Start with the white chocolate buttercream. In the bowl of a stand mixer fitted with the paddle attachment, or with a handheld electric mixer, mix the softened butter until whipped and smooth, about 30 seconds. Add in the powdered sugar and 1 tablespoon of cream, mixing slowly until starting to combine. Measure 1/2 cup of the remaining white chocolate ganache and then add it to the mixing bowl. Turn the mixer to high and mix until smooth. If the buttercream seems a bit dry, add the extra tablespoon of cream.
7. Thoroughly scrape out the bowl of white chocolate buttercream and add it to a piping bag or another bowl. Start the chocolate buttercream by adding the softened butter to the bowl and mix on high, about 30 seconds. Add the powdered sugar, cocoa powder and 1 tablespoon of cream and mix again, starting on low and then turning it up to high. Add in the vanilla, salt and the additional tablespoon of cream, if needed. Mix on high until whipped and smooth, and spreadable.
8. Frost the tops of the cupcakes by alternating the different buttercreams, or using a two-toned approach with a piping bag. There is additional details on this in the blog post above. Serve the cupcakes immediately, or keep them at room temperature, in a sealed container, for 1-2 days. They will keep for 4-5 days in the fridge.

Unfrosted cupcakes can be frozen in an airtight container for up to 2 months, thawing overnight in the fridge.