1 cup all-purpose flour
2/3 cup unsweetened cocoa powder
3/4 teaspoon double-acting baking powder
3/4 teaspoon salt
2 large eggs
1 cup granulated sugar
3/4 stick (6 tablespoons) unsalted butter, melted and cooled
1/2 cup milk
1 teaspoon vanilla extract
1/2 cup chopped walnuts
3/4 cup firmly packed light brown sugar
1 1/3 cups boiling water
Accompaniment: coffee ice cream
Preheat the oven to 350 F. Into a bowl sift together the flour, 1/3 cup of the cocoa powder, the baking powder, and the salt. In another bowl whisk together the eggs, the granulates sugar, the butter, the milk, and the vanilla, add the flour mixture, and stir the batter until it is just combined. Stir in the walnuts and spread the batter evenly in an ungreased 8-inch-square baking pan. In a bowl whisk together the remaining 1/3 cup cocoa powder, the brown sugar, and the water, pour the mixture over the batter, and bake the cake in the middle of the preheated oven for 35 to 40 minutes, or until a tester comes out with crumbs adhering to it.
Serve the cake hot with the ice cream.