Preheat oven to 350ºF.

Prepare a 9x13-inch baking dish by spraying it with non-stick cooking spray. Set aside.

In a large mixing bowl, add cake mix, eggs, milk, vegetable oil, and vanilla. Beat well until smooth.

Transfer batter to your prepared baking dish.

Bake for 30-35 minutes or until a toothpick comes out clean.

Allow cake to cool completely. When cake is cool enough, place it in your freezer for 30-60 minutes, allowing it to harden.

In a large mixing bowl, add marshmallow fluff, butter, powdered sugar, heavy cream, vanilla, and salt. Beat well until smooth.

Place ½ cup of the marshmallow mixture in a small ziplock baggie and save for later.

Place chocolate chips in a small mixing bowl. Set aside.

Place the heavy whipping cream in a microwave safe cup and heat it for 1 minute.

Gently pour heated whipping cream over chocolate chips. Allow to sit for 3 minutes.

Add butter and vanilla. Whisk until smooth.

Allow frosting to cool for 15 minutes or until it thickens. Placing the frosting in the refrigerator will speed this process up.

Remove cake from freezer and gently flip it onto a large cutting board or platter.

Cut the cake in half, lengthwise. Carefully remove the top half and set it aside.

Spread the marshmallow mixture evenly over top of the bottom layer.

Carefully place the top layer of cake on top of the marshmallow filling.

Cover the cake with plastic wrap and refrigerate it for 30 minutes.

Remove cake from refrigerator.

Spread frosting evenly over cake.

Cut a small corner off the ziplock bag with your reserve marshmallow mixture. Carefully pipe the loop design on your cake.

Serve and enjoy!