Preparing the Filling: In the morning or a day ahead, prepare the filling so it has time to set up.
In small saucepan combine milk and cream and bring to a boil. Turn off heat.
In a separate bowl, beat eggs and sugar together until smooth. Add a small ladle of hot cream to the egg mixture to temper; beat to incorporate. Add another ladle and repeat.
Add tempered egg mixture to cream. Turn the heat back on but do not bring to a boil. You want about 170 degrees (212 degrees is boiling). Remove from heat, mix in chocolate and whisk until blended and shiny. Cover with plastic wrap so the chocolate does not form a skin and store at room temperature.
Preparing the Cake: Prepare three 8-inch round cake pans. Spray with vegetable spray and line with a parchment paper round on the bottom. Set aside.
In a medium bowl combine flour, cocoa powder and baking soda to a bowl; stir to blend.
In a large bowl combine oil and sugar. Whisk to blend. Add eggs and whisk; add vanilla and whisk. Add one-third of dry mixture and blend in with a spatula. Add another one-third of the dry mixture and blend inches Add a little of the buttermilk to thin out the batter, blend, then add the remaining dry mix and incorporate. Add the remaining buttermilk and mix inches.
Divide batter equally between the three pans. Tap pans on the counter to knock out any air bubbles. Bake at 350 degrees in the middle to lower half of your oven for 20 minutes or until toothpick placed in middle of cake comes out clean.
Cool cakes and remove from pans. Cut each layer of cake in half horizontally (you'll have 6 layers now). A turntable cake stand is invaluable here. Spread bottom layer generously with filling, starting in the center and pushing it out to the edge. Repeat with all layers. Then frost the top with filling, then sides.
The frosting doesn't need to be perfect. Cover the frosting on the top and sides with shaved milk chocolate for a professional look. Use a spatula or bowl scraper to shave the chocolate (milk chocolate is best as it's softer). Garnish the cake with fresh berries, a mint sprig and chocolate curls.