Bakery Style Whoopie Pie Cake

I found this recipe on a website for parents. The original was for the actual Whoopie pies, but I am too lazy for all of that. I altered a little and made a cake out of it. It is awesome and so worth the work. Note: use real butter, makes it much better.

• Ready In: 40 mins
• Serves: 6

Ingredients

• For Cake

• 1 (18 ounce) box  devil's food cake mix
• 3  eggs
• 1⁄2 cup buttermilk
• 1⁄4 cup  oil
• 1⁄2 cup water

• For Filling

• 12  tablespoons unsalted butter, softened but still cool (1 1/2 sticks)
• 1 1⁄4 cups confectioners' sugar
• 1 1⁄2 teaspoons vanilla extract
• 1⁄8 teaspoon table salt
• 2 1⁄2 cups marshmallow cream

Directions

1. For the cakes: Heat oven to 350°F; line 2 cake pans with parchment paper.
2. Combine all cake ingredients and mix.
3. Pour half of batter into each cake pan. Cook approximately 20 minutes, or until cakes spring back when pressed. Cool completely on baking sheets, at least 1 hour.
4. For the filling:
5. With electric mixer on medium speed, beat butter and sugar together until fluffy, about 2 minutes. Beat in vanilla and salt. Beat in Fluff until incorporated, about 2 minutes. Refrigerate filling until slightly firm, about 30 minutes. (Bowl can be wrapped and refrigerated for up to 2 days).
6. Spread filling onto one of the cakes. Place other cake on top. Refrigerate in air tight container up to 3 days.
7. This is also good if you heat a can of frosting for 20 seconds and pour over the cake.