• Preheat oven to 350º and position a rack in center of oven. Spray cooking into every crevice of pan. Sprinkle cocoa powder all over inside of pan, taking care to hit every crevice. Invert pan over sink and tap it a couple of times to let any excess fall from pan.
• In a small saucepan, combine butter, cocoa powder, salt and water and place over medium heat. Cook, stirring just until melted and combined. Remove from heat and set aside.
• In a large bowl, whisk together the flour, sugar and baking soda. Add half of the melted butter mixture and whisk until there are no lumps. The mixture will be very thick. Add remaining butter mixture and continue stirring until combined. Add eggs, one at a time, whisking until completely blended. Whisk in the sour cream and the vanilla. Whisk until smooth
• Pour the batter into the prepared pan and bake until a toothpick comes out clean, 40-45 minutes. Let the cake cool in pan, set on a rack for 15 minutes and then invert onto rack. Let cool completely before glazing.

For glaze

• Pour powdered sugar into a bowl. Add milk or half and half and vanilla. Stir to combine. Add more milk/powdered sugar, as necessary. The goal is to be able to pour the glaze from the bowl but have it be firm enough not to puddle at bottom of plate.
• Pour glaze from bowl or from a large spoon in a pattern over top and down sides of cake. Immediately douse cake with sprinkles. The more the merrier. Enjoy!