In the bowl of your Kitchen Aid equipped with the whisk attachment, whip the butter until creamy. Add the sugar slowly and incorporate well. Add egg yolks one at the time.
With the motor running at slow speed, add the flour and then the milk. Add baking powder.
Beat the egg whites to soft peaks and incorporate them slowly to the flour mixture. Divide the creamy mixture into two bowls and add dark powder chocolate to one of the bowls. Mix well.
Butter the individual bundt cakes and sprinkle flour to coat them. Discard the excess.
Alternate dropping one tablespoon of cream mix and one tablespoon of chocolate mix until it reaches 3/4 of the way up the mold. With a toothpick, swirl the two batters together ever so gently.
Bake in the oven for about 30 minutes, then do the toothpick test: insert a toothpick into the middle; it should come out clean.
Remove from teh oven, wait to cool off 5 minutes then unmoild and place your cakes over a rack to completely cool off.
Have all your ingredients ready: Baking moves quickly, and measuring everything before you begin makes the process much easier.Do not overmix the batter: Mix only until the ingredients are combined so your cakes stay light and tender.Create gentle swirls: Use a knife or skewer to lightly swirl the vanilla and chocolate batters together. Too much mixing will blur the marble effect.Grease the molds well: Make sure every little curve of the Bundt molds is coated so the cakes release beautifully.Watch the baking time: Individual cakes bake quickly, so check them a few minutes before the suggested time.Let them cool before removing: Give the cakes a few minutes to rest in the molds before turning them out. This helps prevent them from breaking.Add a simple finishing touch: A light dusting of powdered sugar is all they need before serving.
Giangi's Kitchen provides nutritional information, but these figures should be considered estimates, as a registered dietician does not calculate them.