Bakery Style Whoopie Pie Cake - cooking recipe

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

Preparation

For the cakes: Heat oven to 350\u00b0F; line 2 cake pans with parchment paper.
Combine all cake ingredients and mix.
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.
For the filling:
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).
Spread filling onto one of the cakes. Place other cake on top. Refrigerate in air tight container up to 3 days.
This is also good if you heat a can of frosting for 20 seconds and pour over the cake.