Position a rack in the middle of an oven; preheat the oven to 350 degrees. Butter a 23 cm square baking pan. Place the chocolate in a small heatproof bowl or the top pan of a double boiler. Set over a pan of gently simmering water but not touching the water. Stir until melted and smooth. Let cool slightly. Combine the butter and half of the granulated sugar in a bowl. Using a whisk or an electric mixer set on high speed, beat until light and fluffy, 7-8 minutes with the whisk or 4-5 minutes with the mixer. Sift together the sifted flour, baking powder and salt onto the butter mixture and then add the milk. Stir with the whisk or the mixer on low speed until well mixed. Using a rubber spatula, fold in the chocolate and 1 teaspoon of the vanilla. Spread the mixture evenly in the prepared pan. In the same bowl (no need to wash it if you have scraped it clean), stir together the remaining granulated sugar, the brown sugar and cocoa. Sprinkle over the batter in the pan. Add the remaining 1 teaspoon vanilla to the boiling water and pour slowly over the batter so as not to disturb it too much. Bake until the top is firm, about 1 hour. Let cool slightly. To serve, cut into squares. Spoon some of the sauce from the pan bottom over each serving. Serves 8. Source Williams-Sonoma Kitchen Library Cookbook-Chocolate ----