Step 1

Preheat oven to 350 degrees and spray a 18x13-inch pan with baking spray with flour.Or you can butter and flour the pan.

Step 2

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

Step 3

Add butter, cocoa powder, and water to a medium saucepan. Heat until mixture comes to a boil. Stir well and pour over flour mixture.Stir into flour mixture.

Step 4

Add vanilla, sour cream, and eggs. Mix until evenly combined.

Step 5

Transfer batter to prepared pan and bake for 20 to 25 minutes. Let cool.

Step 6

To make frosting, use a hand-held or stand electric mixer to beat peanut butter and butter until creamy.

Step 7

Add remaining ingredients and beat on high for 2 to 3 minutes.

Step 8

Spread frosting on cake.