Just like clockwork, every August I crave old back-to-school lunchbox favorites. Yes, I know I am a childless adult who is more than a decade away from her last first day of school, but I guess it’s pavlovian. In years past, it’s been peanut butter & jelly and Rice Krispies Treats. This time around, it’s arguably the second* best packaged sandwich cookie out there: Oatmeal Creme Pies.

*Oreos are first, obviously.Now, I already have a recipe for a homemade version of Oatmeal Creme Pies—two actually—but this is a non-traditional school year and I think that warrants a non-traditional recipe. Nothing radical, nothing complicated. We’re talking all the flavor, soft texture and marshmallow magic of Oatmeal Creme Pies, but less than half the work.Oatmeal Creme Pie Bars, y’all! These sweet squares are a cross between a thick cookie and a blondie topped with a soft & swoopy marshmallow frosting, and they taste *just* like your favorite school lunchbox treat. Yesssss.The cookie layer is a streamlined version of my usual Oatmeal Creme Pie dough, made with quick oats (homemade or store bought) and a hint of cinnamon. The only “major” change is the addition of a tiny spoonful of baking powder for a little extra lift. The batter comes together in minutes before being spooned into a pan, then baked until golden at the edges and nearly cakey in the middle, the way all good Oatmeal Creme Pies are.The marshmallow frosting is a take on my usual Oatmeal Creme Pie filling. It’s super smooth and a bit glossy in the best possible way. In the past, I’ve used shortening in my Oatmeal Creme Pie filling for maximum nostalgia, but swapped it for butter here with good results.

Heads up that this frosting will not “crust” or set in the same way as a traditional American buttercream, but a brief chill helps it to slice cleanly. It should be soft but not runny, and completely irresistible. With both marshmallow fluff and confectioner’s sugar, it will seem too sweet, but keep in mind that the cookie bar base is pretty light on sugar compared to most, so the end result will be pretty balanced. I mean, it’s still dessert, but it’s not cloying.This batch of Oatmeal Creme Pie Bars came together in a relative flash—less than two hours top to tail, including cooling—meaning you might have time to whip some up soon, regardless of the fact that lunchboxes may not be a part of your life right now, whether it be because school is virtual or because you’re a 35 year old childless adult with a snack cake habit.

That said, I have it on good authority that after-school/afternoon snacks apply at all ages.

Oatmeal Creme Pie Bars
makes one 8- or 9-inch pan, about 16 bars

Bars:
3/4 cup all-purpose flour
1 1/2 teaspoons cornstarch
1/2 teaspoon ground cinnamon
1/4 teaspoon baking powder
1/4 teaspoon baking soda
1/2 teaspoon Kosher or sea salt
1/2 cup (1 stick) unsalted butter, softened to room temperature
2/3 cup dark brown sugar, packed
1 large egg + 1 large egg yolk, room temperature
1 teaspoon real vanilla extract
3/4 cups quick oats*

Marshmallow Frosting:
1/2 cup (1 stick) unsalted butter, softened to room temperature
7 ounces marshmallow fluff (about 1 1/2 cups)
1 1/2 cups confectioner’s sugar
1/2 teaspoon Kosher or sea salt
1 teaspoon real vanilla extract

Preheat oven to 350F. Grease an 8- or 9-inch square pan. Line with parchment, leaving some overhang on two sides for removal. Grease again. Set aside.

In a small bowl, whisk together flour, cornstarch, cinnamon, baking powder, baking soda and salt. Set aside.

In a medium mixing bowl, use an electric mixer to beat butter until light and fluffy, 60-90 seconds. Beat in brown sugar, followed by egg and yolk and vanilla. Add dry ingredients and mix to combine. Mix in quick oats.

Spoon batter into the pan and spread in an even layer all the way to the edges. Bake 20-22 minutes, or until a toothpick inserted in the center comes out clean. Let bars cool completely in their pan on a rack.

Make the marshmallow frosting. Cream the marshmallow fluff and shortening with an electric mixer until light and fluffy. Beat in confectioner’s sugar and salt. Add in vanilla and mix on high until the frosting is very fluffy.

Spread frosting over the top of the cooled bars. Chill for 30 minutes to set. Frosting will not harden.

Run a thin knife around the edge of the pan, then use the parchment overhang to lift the bars onto a cutting board. Use a large, sharp chef’s knife to slice bars, wiping clean between cuts. Serve.

Leftovers may be kept covered at room temperature for a couple of days, or in the refrigerator for up to a week. Ideally, they should be kept in one layer, but if stacking, place layers of parchment or wax paper between.

Note:

If you don’t have quick oats, you may blitz 1 cup of old-fashioned oats in the food processor until there are no whole oats visible. Steel cut oats will not work in this recipe.