01 -
Preheat oven to 350°F. Butter two 6-inch cake pans and line them with parchment paper. Set aside.
02 -
In a small bowl, combine chopped chocolate and cocoa powder. Pour in boiling water and whisk until smooth. Let cool.
03 -
In the bowl of a stand mixer fitted with a paddle attachment, cream together butter and light brown sugar until fluffy. Add eggs one at a time, mixing until incorporated. Mix in sour cream and vanilla extract.
04 -
In a medium bowl, whisk together all-purpose flour, cake flour, baking powder, and sea salt.
05 -
Add flour mixture in thirds to the butter mixture, alternating with the chocolate mixture, beginning and ending with the flour. Mix between additions, scraping down the bowl as needed.
06 -
Divide batter evenly between prepared pans. Bake for 30 minutes, rotating pans halfway through. Cakes are done when a toothpick inserted into the center comes out clean. Let cool in pans briefly before transferring to a wire rack to cool completely.
07 -
In the bowl of a stand mixer fitted with a paddle attachment, beat confectioners' sugar, cocoa powder, softened butter, and kosher salt until smooth. Add heavy cream and mix until fully incorporated.
08 -
Level cooled cake layers. Place one layer on a serving plate or cake turntable. Spread a layer of buttercream over the top. Add the second layer and cover the entire cake with a crumb coat. Refrigerate for 20 minutes before applying a final buttercream layer.
09 -
Mix cocoa powder and vanilla extract until smooth. Dip a food-grade brush into the mixture and flick over the frosted cake to create a speckled effect. Decorate with chocolate shavings and mini chocolate eggs.