What you need:
2 1/4 cups all purpose flour
1 1/2 teaspoons baking powder
1/2 teaspoon salt
4 tablespoons unsalted butter, at room temperature
4 tablespoons vegetable shortening
1/2 cup granulated sugar
1/2 cup packed brown sugar
2 large eggs
1/2 cup buttermilk
2 tablespoons milk
1 teaspoon baking soda
1 teaspoon white vinegar
1/2 teaspoon vanilla extract
1 cup mini chocolate chips
What to do:
Preheat oven to 350 and line 2 baking sheets with parchment paper.
Sift together the flour, baking powder, and salt.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter, shortening, and both sugars and beat until light and creamy, about 3 minutes. Add the eggs and buttermilk and beat until combined.
In a measuring cup, combine the milk, baking soda, and vinegar. Add the milk mixture to the batter along with the flour mixture and beat on low until just combined. Add the vanilla and beat on medium for about 3 minutes, until completely combined.
Using a wooden spoon, stir in the chocolate chips until just incorporated.
Using a spoon, drop about 1 tablespoon of batter onto one of the prepared baking sheets and repeat, spacing them out at least 2 inches apart. Bake one sheet at a time for about 10 minutes each or until the cakes begin to brown. Remove from the oven and let the cakes cool on the sheet for at least 3 minutes before transferring them to a rack to cool completely.
Classic Marshmallow Filling:
1 1/2 cups Marshmallow Fluff
1 1/4 cups vegetable shortening
1 cup powdered sugar
1 tablespoon vanilla extract
In the bowl of a stand mixer fitted with the paddle attachment, beat together the Marshmallow Fluff and the vegetable shortening, staring on low and increasing to medium speed until the mixture is smooth and fluffy, about 3 minutes. Reduce mixer speed to low, add the confectioners' sugar and the vanilla, and beat until incorporated. Increase mixer speed to medium and beat until fluffy, about 3 minutes more.
Pipe or spoon filling onto flat side of cookie and top with another cookie. Roll the edges in sprinkles, if desired.