potato milk (watch the video to see exact quantity)
butter - watch the video to see (a little bit for water bath and mixing with chocolate)
chocolate - watch the video to see (melted and cooled)
sugar - watch the video to see (two-thirds used initially, some sprinkled while whipping eggs)
egg yolks - watch the video to see (used in the sugar mixture)
egg whites - watch the video to see (implied by eggshell handling, quantity unknown)
Instructions
Prepare water bath: Put a water bath over the baking pan with a little bit of butter.
Melt chocolate and butter: Melt the chocolate and butter together in a bowl and let it cool slightly.
Whisk egg yolks and sugar: In a large bowl, whisk two-thirds of the sugar with the egg yolks until creamy and foamy, sprinkling some sugar while whipping.
Combine chocolate with egg mixture: Add the cooled chocolate and butter mixture into the egg yolk and sugar foam and mix well.
Prepare batter: Use the large bowl to mix the batter thoroughly. Divide the batter into two parts, placing half aside.
Assemble cake: Pour the batter into the baking pan prepared with the water bath.
Bake: Bake the cake at 175°C (347°F) for about 30 to 40 minutes.