Preheat oven to 350°F. Grease and flour a 9x13” baking pan.
In a large mixing bowl, combine flour, sugar, cocoa powder, baking soda and salt. In a large liquid measuring cup, combine eggs, milk, vegetable oil and vanilla extract. Add the wet ingredients to the dry and beat with an electric mixer on medium for 1 minute. Stir in the boiling water and transfer the thin batter to a prepared baking pan.