Chocolate Magic Custard Cake

"Wow, just took this out of the oven & had to sneak a bite — wonderful.!.
Seems several folks couldn’t get it right.it's wonderful thing by recipes and I for one do appreciate it. I’m diabetic so used Splenda, and it’s great."

Ingredients

4 eggs, at room temperature
1 teaspoon vanilla powder or extract
1 and ¼ cup sugar
110g butter (1/2 cup), melted
½ cup all purpose flour
⅓ cup unsweetened cocoa powder
2 cups milk, lukewarm
1 tablespoon powdered sugar for dusting

Instructions

Preheat oven to 320F (160C).
Grease a 30cmx17cm or 9x9 inchbaking pan and line it with parchment paper.
Separate egg whites and yolks.
Beat egg whites in a bowl until stiff and put aside.
Whisk egg yolks, vanilla powder and sugar until creamy.
Add melted butter and mix for half a minute.
Add the flour and unsweetened cocoa powder. Mix with a spatula until incorporated well.
Pour the milk gradually and continue beating.
Add in the egg whites, one third at a time and gently stir with a spatula. Don't overmix, just stir a few times.
Pour this liquidy batter into the baking pan and bake for 60 minutes.
Let it cool and when it comes to room temperature chill for an hour.
Slice it in the size you like and dust with powdered sugar right before serving.
Keep it in refrigerator until you finish it all.