Preheat the oven to 350º F. Grease a 9 by 13-inch baking pan with 1 teaspoon of the shortening.

In a large, heavy saucepan over medium heat, melt the remaining 1 cup shortening. Remove from the heat and let cool slightly. Add the sugar and blend. Add the eggs one at a time, whisking after each addition. Add the water and vanilla and whisk to mix well. Add the flour, cocoa, baking powder, and salt and stir to blend. Fold in the walnuts and chopped chocolate, then spread the batter evenly in the prepared pan.

Bake until the brownies spring back when touched, about 25 minutes. Remove from the oven and let cool for 30 minutes.

Spread the icing over the cake with a rubber spatula. Let cool completely before cutting into squares to serve.