Chocolate Peanut Butter Cookie Bars start with a layer of super soft & chewy peanut butter cookie, and are topped with creamy milk chocolate frosting.
These are like a classic Peanut Butter Cookie in the form of a bar dessert. Our favorite Chocolate Buttercream makes for a delicious topping for these cookie bars as well!
PEANUT BUTTER + CHOCOLATE COOKIE BARS
Hi! My name’s Fiona and I’m so excited to meet you! I blog over at Just So Tasty, and today’s my first post on Lil’ Luna.
I love baking desserts, and anything with peanut butter – especially peanut butter and chocolate. So, I thought it only made sense to share my favorite Chocolate Peanut Butter Cookie Bars.
These cookie bars start with a layer of soft and chewy peanut butter cookie. Then they’re frosted with creamy milk chocolate frosting, and decorated with Reese’s Pieces.
The chocolate frosting makes them a little more special than regular peanut butter cookies. And because we’re making them in bar form, there’s less busy work since we don’t have to roll the dough into balls.
How to make Peanut Butter Cookie Bars
PREP. Preheat the oven to 350. Line an 8×8 inch square baking pan with aluminum foil, then grease with non-stick cooking spray. Set aside.
DOUGH. In a medium bowl using an electric mixer on medium speed, beat together the butter, sugar and peanut butter until smooth. Add in the egg and vanilla and continue beating until combined (about 30 seconds).
Turn the mixer down to low speed and carefully beat in the flour, cornstarch and baking powder. You may need to turn off the mixer and scrape down the sides of the bowl.
BAKE. Spoon the batter into your prepared pan, and press down to the edges using your hands or a rubber spatula. Bake in your preheated oven for 20-23 minutes or until the top is set and the edges are just starting to brown and pull away from the sides of the pan. Allow to cool fully before frosting.
FROSTING. Make the frosting in a medium bowl using an electric mixer on medium speed. You can adjust the amount of confectioners sugar or whipping cream to reach the desired consistency.
(Note: I like to use whipping cream in frosting because it makes it extra creamy and smooth. But if you only have milk on hand, it’ll work too.)
DECORATE. To decorate the bars, first lift them out of the pan using the aluminum foil. Frost with the chocolate buttercream using a flat-edge knife. Then decorate with Reese’s Piece. Cut into 9-12 bars and serve.
Variations + Additions
It’s important to mention that these bars bake best when regular peanut butter is used. The natural or whipped kind just do not turn out as well. You can, however, use regular crunchy peanut butter if you like a bit of texture.
These Peanut Butter Bars are delicious as is, but it can be fun to change things up every now and then. Here are a few suggestions that you might like to try:
- Press mini reese’s cups into the top of the dough before baking
- Mix in mini chocolate chips with the dough
- Use crunchy peanut butter or top with crushed nuts
Making Ahead & Storing
These Peanut Butter Cookie Bars are best when eaten right way. If you happen to have leftovers, they can be STORED in an airtight container for up to 4 days.
If you want to make them ahead of time, then I would suggest whipping up the dough and freezing it in dough form.
Shape the dough into a ball or log. Wrap tightly with plastic wrap and again with foil. Label and freeze for up to a month. Thaw in the fridge before pressing into a baking pan to bake according to directions.
The chocolate frosting can also be frozen in an airtight container. Thaw before using.
For more chocolate + Peanut butter treats, check out:
- Peanut Butter M&M Cookies
- Peanut Butter Cup Cookies
- Mini Peanut Butter Cookies
- Frozen Peanut Butter Pretzel Pie
- Reeses Pieces Bars
- Reeses Brownies
- Chocolate Peanut Butter Cookies
Peanut Butter Cookie Bars Recipe
Peanut Butter Cookie Layer
- 1/3 cup unsalted butter softened to room temperature
- 2/3 cup brown sugar packed
- 1/3 cup creamy peanut butter not natural or whipped
- 1 1/2 tsp vanilla extract
- 1 large egg
- 1 cup all purpose flour
- 2 tsp cornstarch
- 1/2 tsp baking powder
Milk Chocolate Frosting
- 1/3 cup unsalted butter softened to room temperature
- 1 1/4 cup powdered sugar sifted
- 3 tbsp natural cocoa powder sifted
- 1 tsp vanilla extract
- pinch salt
- 2-3 tbsp heavy whipping cream
- Preheat the oven to 350F degrees. Line an 8x8 inch square baking pan with aluminium foil, then grease with non-stick cooking spray. Set aside.
- In a medium bowl using an electric mixer on medium speed, beat together the butter, sugar and peanut butter until smooth and no butter or sugar lumps remain. Add in the egg and vanilla and continue beating until combined (about 30 seconds).
- Turn the mixer down to low speed and carefully beat in the flour, cornstarch and baking powder. You may need to turn off the mixer and scrape down the sides of the bowl.
- Spoon the batter into your prepared pan, and press down to the edges using your hands or a rubber spatula. Bake in your preheated oven for 20-23 minutes or until the top is set and the edges are just starting to brown and pull away from the sides of the pan. Allow to cool fully before frosting.
- To make the frosting, in a medium bowl using an electric mixer on medium speed beat the butter until softened. Turn the mixer down to low speed and beat in the confectioner's sugar about ½ at a time. After each addition has been incorporated, turn the mixer up to medium high speed for 5 seconds. Then with the mixer on low speed, beat in the cocoa, vanilla and salt. Finally, beat in the whipping cream 1 tablespoon at a time until you get your desired consistency and sweetness level.
- To decorate the bars, first lift them out of the pan using the aluminium foil. Frost with the chocolate buttercream using a flat-edge knife. Then decorate with Reese's Piece. Cut into 9-12 bars and serve.
I’m thoroughly convinced that chocolate and peanut butter are the ultimate combo! These cookie bars look AMAZING! Thanks for sharing this recipe with us, Fiona. For more awesome recipes, visit her over at Just So Tasty!
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Wow. Just wow. So peanut butter-y. The perfect touch of chocolate. And heck, let’s just throw one of the world’s best candies right on top. I need these in my life right now!
Right?! I need them too!! Thanks for stopping by!!
These were very good. The cookie wAS perfectly soft and had a great peanut butter flavor. The frosting was just a lIttle too sweet for us, so I spread it in a thin layer over the coOkies, which made them perfect for my while family.
Thank you for sharing that! I am glad your family liked them 🙂
This recipe is the perfect size to make in a toaster oven tray:) Life saver since my oven went out! And my family loved it! Very soft and perfectly balanced in sweetness!
Sorry about your oven! Thank you for letting me know 🙂
Just like the cookie but in a bar form instead. Same great taste.
I could eat the whole pan! Reeses are mine & my son’s favorite! These are the creamiest bars & so, so good!
Thank you so much for sharing you very genius idea for this cookie bars! I really loved that looks and taste of it!
You’re welcome! So glad you enjoyed the bars!
I love anything with Peanut Butter and Chocolate! I know that I have to make these to share with others, because I could eat an entire pan of these. So addicting. I love the creamy frosting and chewy peanut butter together!
Mmm yes, that chocolate frosting and PB combo is to die for!
So decadent & delicious!! The bars are so creamy. Peanut butter & chocolate are my favorite combination!
Wow Fiona, these were absolutely delicious! There’s nothing better than peanut butter and chocolate. And what a yummy way to top off these bar cookies than with Reeses Pieces!
Thank you!! I’m so glad you enjoyed them!
I’m a sucker for the chocolate peanut butter combo. This recipe is definitely a keeper.
These are always gone in a matter of minutes. So soft and chewy but lots of flavor!
Good grief these are so good! Sinfully good! Hubs said they would be gone by morning. Ha! (That’s the BEST compliment too!)
Oh thank you!! I’m so happy to hear you all enjoyed the cookie bars!