Preheat the oven to 350°F and separate the eggs. Beat the egg whites, gradually stir in the sugar, and then beat the mixture into a firm meringue. Gradually mix in the egg yolks. Sieve the flour, cocoa powder, and baking powder into the egg mixture. Finally, gently stir the milk into the mixture.
Grease a 4-quart saucepan with butter and dust it with flour. Knock out the flour and pour the chocolate cake batter inside. Put the saucepan in the oven and bake for 90 minutes. Meanwhile, prepare the white chocolate filling. Boil the heavy cream over medium heat, add the white chocolate chips and continuously stir until the chocolate has melted, puree with a hand blender until a smooth cream forms, and then let cool down a bit.
Cut off the top of the baked cake for an even surface, slide the cake out of the saucepan onto a serving platter, and let cool.
Cut the cake horizontally into 3 even sections.
Use a tall shot glass to punch out 5 holes in the top of the cake and save the removed cake crumbs for later.
Make a hole in the middle of the cake, but leave the shot glass inside for now. Cut off the bottom of a 2L plastic bottle and place it with the opening facing down in the middle of the cake.
Carefully pour about ¼ of the liquid white chocolate filling into the middle of the bottom of the bottle so that it flows evenly into all 5 cake holes.
Slightly rotate the upper 2 cake tiers and repeat the process with next ¼ portion of the liquid white chocolate filling.
Finally rotate just the top cake tier and repeat the process with the next ¼ portion of the liquid white chocolate filling.
Remove the plastic bottle and the shot glass with cake from the middle and pour the remaining quarter of the white chocolate filling into the empty hole.
Spread whipped cream over the entire cake, sprinkle the cake crumbs from earlier on top, and garnish with fresh berries and white chocolate flakes.
