f you’re as obsessed with Little Debbie Oatmeal Cream Pies as I am, you’re going to fall hard for these Oatmeal Cream Pie Cookie Bars. Imagine a thick, chewy oatmeal cookie base with warm notes of cinnamon and molasses, topped with a pillowy, marshmallow buttercream that tastes like childhood—but better. These bars are everything we love about the classic snack, but elevated in flavor and texture, with no shortening in sight.
Whether you’re baking for a crowd, a lunchbox treat, or just a cozy weekend at home, these bars hit all the right notes: nostalgic, soft, sweet (but not too sweet), and ridiculously easy to make.
Recipe Tips
- Don’t skip the molasses! It adds the depth and chew that makes these bars taste like the real deal.
- Quick oats vs. old-fashioned: You can use either, it all depends on what kind of texture you want! Quick oats give a more uniform texture; old-fashioned oats give a little more bite, chew & texture.
- Store them chilled: These bars keep well in the fridge for up to 5 days. Just let them sit at room temp a few minutes before eating for the best texture.
If you’re hosting a gathering or looking for a make-ahead dessert, these bars are a total win. Unlike sandwich-style oatmeal cream pies that need individual assembly, these cookie bars are all baked in one pan and topped once cooled—making them simple, shareable, and stress-free. They slice beautifully and hold up well on dessert tables, in lunchboxes, or wrapped up as sweet little gifts.
HOW TO GET CLEAN SLICES
This is a question I get all the time so I wanted to write out exactly what I do to get these clean slices every time! After assembling the bars I chill completely for at least 45 minutes. After chilling the bars, fill a large glass with hot water. I typically use a large Stanley or travel mug. Place a large, sharp knife (not serrated) in the hot water for 1 minute. right before cutting pull the bars out of the fridge. Wipe the knife with a paper towel or towel and immediately slice. You do not want any water transferring onto the dessert. Repeat for each slice, allowing the knife to get hot again by placing in the water for 10-15 seconds. That’s how I get picture perfect slices every time 🙂
You can also customize the bars to suit your mood or the season. Try adding a pinch of nutmeg or cloves for a cozier fall flavor, or swap the vanilla extract in the frosting for maple or almond for something different. You could even sandwich two thin bars together for a twist on the classic. However you enjoy them, one thing’s for sure—these bars never last long in our house!
These Oatmeal Cream Pie Cookie Bars are like a nostalgic hug in dessert form. They’re easy to make, deeply satisfying, and guaranteed to disappear fast. If you give them a try, let me know how they turn out—or tag me @mymessykitchenn on Instagram. I’d love to see your version!
Oatmeal Cream Pie Bars
Ingredients
For the bars:
- 1 cup salted butter melted
- ⅔ cup light brown sugar
- ½ cup granulated sugar
- 2 tsp vanilla extract
- 1 tbsp unsulphured molasses
- 2 eggs room temperature
- 1 ½ cups all-purpose flour
- 1 tbsp corn starch
- 1 tsp baking soda
- 1 tsp ground cinnamon
- ½ tsp kosher salt
- 3 cups old fashioned oats You can also use quick oats for a softer, more uniform texture in the bars
For the frosting:
- ¾ cup salted butter room temperature
- 1 cup marshmallow creme
- 2 ½ cups powdered sugar
- 1 tsp vanilla extract
- ½ tsp salt
- 1-2 tbsp heavy cream or milk room temperature
- extra cinnamon for dusting the top
Instructions
For the bars:
- Preheat your oven to 350°F. Line a 9×13-inch pan with parchment paper and lightly grease. In a large mixing bowl, whisk together melted butter, brown sugar, granulated sugar, and molasses until smooth.
- Add eggs and vanilla and whisk again until fully combined. In a separate bowl, stir together the flour, cornstarch, baking soda, cinnamon, and salt. Add the dry ingredients to the wet ingredients and mix just until combined. Fold in the oats.
- Spread the dough evenly into the prepared pan and smooth the top. Bake for 25 minutes, or until the edges are golden and the center is just set. Let cool completely before frosting.
For the frosting:
- Beat the softened butter until smooth and creamy. Add the marshmallow creme and vanilla and beat until light and fluffy. Gradually mix in the powdered sugar and a pinch of salt. If needed, add a tablespoon or two of heavy cream for a spreadable consistency.
- Spread the marshmallow buttercream evenly over the cooled cookie bars. Lightly dust with ground cinnamon for that extra oatmeal pie magic.
- For cleaner slices, refrigerate the bars for 20–30 minutes before cutting into squares.