Position a rack in the center of the oven and preheat the oven to 350 degrees. Lightly coat a baking pan with cooking spray.
In a small saucepan, combine the butter and chopped chocolate and set over very low heat until melted. Stir the mixture and set aside to cool. In a medium-sized mixing bowl, whisk together the flour, cocoa, baking powder, salt, cinnamon, and nutmeg. Measure the sugar into the large bowl of an electric mixer and beat in the cooled butter-chocolate mixture. Add the egg plus whites, vanilla, and water and beat well. Add the dry ingredients and mix on low speed just until blended. Don't overbeat. The batter will be thick. Spoon the batter into the prepared pan, smooth the top, and bake for 22 to 25 minutes; 23 minutes is usually right for me. When done, the top will look dry and a wooden pick inserted near the edge will come out with a few crumbs but the center will look slightly gooey. Cool in the pan and cut into squares.
I have been trying for a couple of years to produce a brownie worthy of the name with less fat and less solid chocolate. My taste testers finally agree that this is it - a great brownie they would never suspect of being lower in anything. I have cut the classic 58 percent down to 31 percent calories from fat and eliminated 87 calories, 10 g fat, and 22 mg cholesterol from each brownie.
When traditional proportions are disrupted, textures become moist and cakey at best or dry, insipid, and tough at worst. One rule emerges clearly: The fewer ingredients, the better the brownie. Avoid the usual low-fat stand-ins: applesauce, yogurt, corn syrup, canola oil. Use butter, but less, and replace most of the solid chocolate with rich-tasting Dutch-processed cocoa; retain at least 1 ounce of solid chocolate, however, for a more complex chocolate taste. A few tricks: Cake flour produced a more tender crumb than all-purpose, and melting the butter with the chocolate, as opposed to creaming the solid butter with the sugar, gave a fudgier crumb. A touch of baking powder seems to enhance the crunch of the top crust.
Faced with the choice of adding high-fat chopped nuts or keeping the 1/4 cup butter, there was no contest; nuts put us over the top in fat content. However, if you feel deprived without them, sprinkle about 3 tablespoons of finely chopped walnuts on top before baking; the changes are modest: 33 percent calories from fat, plus 9 calories and 1g fat per brownie.