Position an oven rack in the oven's center and preheat the oven to 325F degrees. Grease a 10-inch Bundt pan.
Sift the cocoa powder, flour, salt and baking powder into a small bowl and set it aside.
In a large bowl, beat the butter and sugar with an electric mixer for several minutes until the mixture lightens in color and becomes fluffy.
Add the eggs, one at a time, mixing until the egg is completely incorporated. Beat in the vanilla.
Scrape down the sides of the bowl with a rubber spatula.
In a small bowl, stir together the sour cream and water.
Mix in the dry mixture and the sour cream mixture alternately in five stages beginning and ending with the flour mixture (i.e. 1/3 of the flour, then 1/2 the sour cream, then 1/3 of the flour, then the remaining half of the sour cream and then the remaining third of the flour). Stop to scrape down the sides of the bowl a couple of times to make sure everything is well incorporated.
Scrape the batter evenly into the prepared Bundt pan.
Bake at 325F degrees until a toothpick inserted in the center comes out with just a few moist crumbs, 60 to 80 minutes. (Mine took about 75 minutes to be done.)
Remove the pan from the oven and set it on a wire rack, allowing the cake to cool completely in the pan. When cooled, turn the cake out onto a cake plate.
Notes
Serving size: 1 slice (1/16th recipe)WW Points: 16Check the WW Points for this recipe and track it in the WW app. (Must be logged into WW on a smartphone or tablet.)14SmartPoints (Green plan)13SmartPoints (Blue plan)13SmartPoints (Purple plan)7PointsPlus (Old plan)Thoughts on Making Recipe Lighter: Replacing 1/2 the butter with buttermilk would decrease the calories to 235 and PointsPlus to 7 and Points to 11.When substituting buttermilk for butter, you can substitute 1/2 cup of buttermilk for every 1 cup of butter. So in this recipe, you'd use 1/2 cup butter and 1/4 cup buttermilk in place of the 1 cup butter.You could also substitute your favorite zero-calorie sweetener for the sugar to lower the points in each slice.