Preheat oven to 350 degrees . In a pan, whisk 2 cups water and the sugar over medium-high heat until the sugar dissolves. Remove from the heat, add the chocolate and butter and let stand 10 minutes; whisk until smooth.
In a bowl, whisk the flour, baking powder, baking soda and salt. Whisk the eggs and vanilla into the chocolate mixture. Add the flour mixture; whisk until smooth. Transfer to prepared foil-lined pans; bake as directed.
The Do's and Don'ts of Cooking with Chocolate