Step 1

Preheat oven to 350F.

Step 2

Grease and flour a 10 x 15 jellyroll pan. (Use cocoa powder to "flour" the pan if you like.)

Step 3

Bring butter, water, and cocoa powder to a boil in a medium saucepan, stirring frequently. Remove from heat and let cool for 10 minutes.

Step 4

Whisk together the flour, sugar, salt and baking soda in a large bowl. Set aside.

Step 5

Whisk together sour cream and eggs.

Step 6

Combine the sour cream and egg mixture with the flour and sugar mixture.

Step 7

Gradually stir in the warm cocoa mixture and mix well. (You might need to whisk together.)

Step 8

Pour the batter into the prepared jellyroll pan.

Step 9

Bake for 22-25 minutes. The center of the cake should spring back when touched.

Step 10

Bring the milk and butter to a boil. Remove from heat.

Step 11

Whisk in the powdered sugar, cocoa powder, salt and vanilla extract.

Step 12

Pour the frosting over the cake while the cake is still warm.

Step 13

Quickly sprinkle on nuts if desired.

Step 14

Leftovers should be stored in airtight container.