In blender add eggs, milk, sugar, vanilla extract, cocoa powder, and flour. Blend until well combined. I find you have to scrape down the sides at least once and blend again. (You can also mix everything by hand as well).
When oven has preheated remove the pan from the oven and add butter. Place back into the oven until the butter fully melted.
Then, pour blended batter into heated pan and bake for 22 minutes.
When you first remove it from the pan it will have raised dramatically but after a few minutes the pancake will sink down.
Enjoy with whipped cream, sweetened cocoa powder, icing sugar, or fruit and syrup.