Step 1

Preheat oven to 350°F. Lightly spray a 9x13-inch baking pan with cooking spray and set aside.

Step 2

In a large mixing bowl, combine the cake mix, melted butter, buttermilk, eggs and vanilla with a hand-held mixer on medium speed until well combined, stopping the mixer to scrape down the sides of the bowl once. Pour the batter into the prepared pan.

Step 3

Bake cake for 40-45 minutes, or until it tests done when a toothpick is inserted near the center. Remove cake from oven and immediately spread the marshmallow creme over the cake.

Step 4

Prepare the chocolate frosting.

Step 5

Melt the butter in a medium saucepan over low heat until melted. Whisk in the cocoa powder and milk. Stirring constantly, bring the mixture just to a boil; immediately remove from the heat and whisk in the powdered sugar until thickened and smooth.

Step 6

Pour the hot frosting over the marshmallow layer and carefully spread the frosting to the edges. Sprinkle the pecans over the top of the cake. Let cake cool completely before serving.