Preheat the oven to 350 degrees . Grease a 9-inch round cake pan; line the bottom with parchment paper and grease the paper.
In a large bowl, whisk together the flour, sugar, cocoa powder, salt and baking soda. Make a well in the center, add the eggs and milk and whisk gently to make a thick batter; whisk vigorously 30 to 40 times. Whisk in the melted butter and vanilla just until smooth. Scrape into the prepared pan.
Bake until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Let cool on a rack for 10 minutes; invert onto the rack, remove the pan and parchment paper and invert again. Let cool completely. Dust with the confectioners' sugar.
The Do's and Don'ts of Cooking with Chocolate
