Oatmeal Cream Pie Bars

Preheat oven to 375°F and spray two 8x12-inch baking pans with nonstick spray (if you don't have two 8x12 pans, use one 12x16-inch pan, and use 1 cup less dough. Line the pan with parchment so that each edge of the pan has a 2-inch over-flap. Spray the parchment with nonstick cooking spray.

Cream

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugars together until creamy. Add eggs and vanilla and beat well.

Whisk

In a medium bowl, whisk the flour, baking soda, cinnamon, nutmeg, and salt together. Add the flour mixture to the wet mixture all-at-once and beat only until flour mixture is incorporated.

Add the oats and mix until incorporated.

Spread

Divide the dough in half and spread half in each pan. Spray a wooden spoon or rubber spatula with cooking spray to prevent the dough from sticking. Work the dough evenly until it reaches across the pans evenly. (If necessary, spray your fingers with cooking spray and spread the dough with your fingers. The dough is somewhat stiff and sticky.)

Bake 12-13 minutes, or until the dough is cooked in the middle and is light golden brown. Do not over-bake or the bars will dry out.

Beat

While the bars bake, make the cream filling: In the bowl of a stand mixer fitted with the whisk attachment, beat the softened butter until fluffy. Add the powdered sugar and beat until lighter in color and smooth. Add the marshmallow fluff, vanilla, and salt. Beat until light and fluffy. Set aside until ready to use.

Cool

Transfer the cookie bars to a cooling rack to cool 10 minutes. Lift the bars out of the pans, by the parchment paper and set them back on the cooling rack to completely cool.

Freeze

When bars are cool, spread the Cream Filling over one of the uncut 8x12-inch cookies. Remove the parchment paper and place the other 8x12-inch cookie over the Cream Filling and press gently down. Place the entire large cookie on a larger baking tray and cover it with plastic wrap and foil. The cookies are easy to cut when frozen. Place in the freezer at least 2 hours or overnight.

Cut the frozen cookie into bars.