Step 1

Preheat the oven to 350 degrees F.

Step 2

In a mixing bowl, combine the flour, the sugar, and the salt.

Step 3

In a saucepan, melt 2 sticks of the butter.

Step 4

Add the peanut butter to the melted butter and stir them together.

Step 5

Add the boiling water to the peanut butter mixture and allow it to boil for 30 seconds.

Step 6

Transfer the peanut butter mixture from the heat, pour it over the flour mixture, and stir to slightly cool it.

Step 7

In a measuring cup, add the buttermilk, the eggs, the baking soda, and 1 teaspoon of the vanilla extract and stir to combine.

Step 8

Pour the buttermilk mixture into the batter and stir to combine.

Step 9

Evenly spread the batter into an 18x13-inch sheet pan and bake the cake until a toothpick inserted into the center comes out clean, about 20 minutes.

Step 10

Melt the remaining butter in a saucepan.

Step 11

Add the cocoa to the butter and stir to combine.

Step 12

Turn off the stove-top heat and stir the milk, the vanilla extract, and the powdered sugar into the cocoa mixture.

Step 13

Add the pecans to the icing mixture and stir until they are evenly distributed.

Step 14

Pour the icing over the cake.

Step 15

Slice and serve.