Preheat oven to 350 degrees. Butter and flour 2 (9 inch) cake pans.

In a bowl of a stand mixer or bowl with a hand mixer cream together butter and sugar until light and fluffy. Beat in eggs one at a time, be sure to scrape the sides of the bowl in between. Beat in the vanilla. Turn off mixer.

In a bowl combine flour, cocoa powder, baking powder, baking soda, and salt. Add mixture to the mixer. Turn mixer on to medium speed and beat for 3 minutes. Beat in pumpkin. Turn mixer to medium-low and pour in hot water. Mix 1 minute.

Pour cake batter evenly into prepared cake pans. Bake in preheated oven for 35 - 40 minutes or until toothpick inserted comes out clean. Allow to cool in the pan for at least 15 minutes. Gently remove cakes from pan and place on cooling rack to cool completely.

While the cake is cooling make the frosting by creaming together butter and 5 cups powdered sugar until fluffy. Beat in milk, vanilla and 1/4 teaspoon salt until the mixture becomes thick and spreadable. If frosting is too thin add remaining 1/2 cup powdered sugar. Adjust salt if necessary.

Place one of the cakes bottom side up on a cake stand. Spread a third of the frosting evenly on the top. Place the other cake, top side up, on top of the frosting. Frost the cake with remaining frosting, using smooth strokes.

Sprinkle sprinkles on the top of the cake until covered. To cover the sides, place sprinkles in the palm of your hand and gently press into the sides of the cake. Repeat until all the sides are covered. Slice and serve.