The BEST Frosted Peanut Butter Oatmeal Bars

Frosted peanut butter oatmeal bars are packed with peanut butter from the bar all the way through the frosting. They are the perfect peanut butter lovers bar cookie.

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Sometimes, I have a hankering for a sweet peanut buttery treat. Don’t get me wrong: I love a good peanut butter and chocolate combination. I have a crazy easy peanut butter cup cookie recipe here on my site. But when the peanut butter craving hits, these frosted peanut butter oatmeal bars really hit the spot! I love the thick peanut butter bars on their own, but adding the peanut butter frosting just takes it over the top.

Want even more peanut butter flavor? There are a few variations you can try to turn these into the ultimate peanut butter oatmeal bars! I’ve included them at the bottom, below the recipe card.

What You’ll Need

Scroll down to the recipe card below this post for ingredient quantities, full instructions and tips for success.

Peanut Butter Oatmeal Bars

• Peanut Butter – You can use smooth or crunchy peanut butter. (For natural peanut butter, see the note in the FAQ section.)
• Oatmeal – Use quick oats for the best result.
• Butter – Salted or unsalted
• Brown Sugar
• White Sugar
• Egg
• Vanilla
• Flour – I use all purpose flour for this recipe.
• Baking Soda
• Peanut Butter Chips – Optional, but highly recommended

Peanut Butter Frosting

The bars are delicious on their own but the peanut butter frosting takes it to a whole other level!

• Peanut Butter
• Powdered Sugar
• Sweetened Condensed Milk
• Milk

Recommended Baking Supplies

• Hand mixer or stand mixer
• Glass mixing bowl
• Metal baking pan: 8×8, 9×9 or 9×13
• Standard measuring cups and spoons
• Push up/adjustable measuring cup (great for peanut butter and shortening)
• Parchment paper

How to Make Frosted Peanut Butter Oatmeal Bars

For the Peanut Butter Oatmeal Bars

Preheat the oven to 350°F. Spray a metal pan with cooking spray. This recipe works well with an 8×8, 9×9 or 9×13 pan. Line your pan with parchment paper, pressing down into the corners and creases. Leave enough parchment paper hanging over that you can use it as a handle to lift it out of the pan.

You can use a glass pan if you want, but this may affect cook times and the texture of the bars.

*NOTE* While you can make this recipe using arm strength (wink), I suggest using a hand mixer or a stand mixer. This will ensure more even distribution of the ingredients, resulting in a better bar.

In a large bowl or stand mixer bowl, combine softened butter, brown sugar and white sugar. Mix until creamy and well combined. Add the egg, peanut butter and vanilla. Beat together until light and fluffy.

Now it’s time to add the dry ingredients: flour, baking soda and oatmeal. Again, mix until well combined. You should expect to have a thick dough, more like cookie dough. At this point, you can add in the peanut butter chips. (I highly recommend it!)

Dump the mixture into your prepared pan. Because it is thicker, you will need to use a silicone spatula or your hands to press it into the pan evenly.

Put the pan into the oven and bake the bars. For an 8×8 pan, bake for 15 minutes. For a 9×9, bake for 16-17 minutes. For a 9×13 pan, bake for 20 minutes. You can check for doneness by using a toothpick inserted a couple inches from the edge. The toothpick should come out with a few crumbs attached to it and the edges should be a light brown.

Remove the bars from the oven and place on a wire rack to cool completely.

For the frosting

Combine peanut butter, powdered sugar and sweetened condensed milk into a bowl or stand mixer. Mix well. Again, I recommend letting a mixer (hand or stand) do the work for you to ensure a smooth, creamy frosting. If you want a runnier frosting, add some milk, 1 Tbps at a time and mix until you get the desired consistency.

When the bars are cool, pour the frosting over the top and spread all the way to the edges. Let the frosting set for 10-15 minutes before removing the bars from the pan. Then cut into squares and serve.

Tips for Success

• Use a parchment paper sling. Lining your pan with parchment paper is a great way to make clean up faster and easier. Plus, it creates “handles” for you to remove the bars from the pan. This makes cutting the bars and serving them super easy. Spraying your baking pan with cooking spray before adding the parchment paper will help the paper stick to the pan (in a good way).
• Don’t overbake. Bars can dry out quickly from overbaking so starting your timer with a little less time is a good way to keep an eye on them. Use a toothpick to check for doneness. It should not come out wet which would indicate the bars aren’t done. But it also shouldn’t come out completely clean. A few crumbs sticking to the toothpick is fine. Because your pan is still hot when you remove the bars from the oven, remember that the bars will continue baking for a bit longer. The bars will still taste good even if they get overbaked. And the frosting will help add some moisture to the finished product. But they may not taste fresh for as long since they started out drier.
• Cool completely. Whether or not you choose to make these bars with frosting, letting them cool completely will make them easier to remove from the pan. It will also make it easier to cut and serve them. A bar that is not hot, or even warm, will help when you are spreading the frosting since it won’t stick to it as you are trying to spread.

Variations

• With or without frosting. I’ve said it once and and I’ll say it again: these bars are so good with the peanut butter frosting! But you can absolutely choose to eat them without the frosting. If you do this, consider adding something to the top. (see suggestions below)
• Add mix-ins. I suggest adding peanut butter chips to the bars to help create the ultimate frosted peanut butter oatmeal bar. But here are some other delicious options: white chocolate chips, chocolate chips (milk, semi or dark), Reese’s pieces candies, chopped Reese’s peanut butter cups or even using chunky peanut butter instead of smooth.
• Decorate the top. Adding something to the top of the bars (frosted or not) is another variation to try. You could use many of the suggestions given for mix-ins and put them on top of the bars instead. Another option is to sprinkle 1 cup of chocolate chips over the top of the bars right after the come out of the oven. Let them melt and then spread them over the bars. Then add the frosting on top of the cooled chocolate.
• Melted butter. Looking for a slightly chewier, more brownie-like texture? Instead of softened butter, you can use melted butter. This will create a more dense bar. Keep in mind that this may affect the bake time, so take that into account if you go with this variation.

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Recipe FAQs

Can I use natural peanut butter?

At your own risk. I have never used natural peanut butter in my own baking. However, I do know that there are some challenges associated with using natural peanut butter in baking. According to America’s Test Kitchen: “You’ve got to stir the peanut butter well just before measuring it—and you’ve got to make sure that you’ve been stirring just as thoroughly all along. Only then will you ensure that the PB going into your dough has the proper ratio of solids to fats.”

Can I use other nut butters?

Yes! Although the peanut butter taste won’t be there and it may affect the texture.

What is the best way to store the bars?

To keep the bars soft, I recommend storing them at room temperature in an airtight container for 3-4 days. Or you can store them in the fridge for up to 1 week. (Let them come to room temperature before serving.) These baking pans with lids are a great solution!

What can I do with the leftover sweetened condensed milk?

Here are a few suggestions of recipes you can use the leftover sweetened condensed milk for:

• Snow cone topping. Have you ever tried drizzling sweetened condensed milk over the top of your snow cone? It’s what they do on the Hawaiian Islands when they make shave ice and it’s delicious! We have a great snow cone machine that is compact, easy to use and easy to clean. It allows us to make snow cones year round! You can check out my full review of our Hawaiian Shaved Ice Snow Cone Maker here.
• Double this recipe for frosted peanut butter oatmeal bars. If you are making this dessert for a crowd, double the recipe! This allows you to use the entire can of sweetened condensed milk. You will need to bake the bars in a larger pan, such as a sheet pan, or you can make extra thick bars in a 9×13 pan. Bake time will vary but I would start with 15 minutes for a sheet pan and 20 minutes for a 9×13.
• Condensed Milk Chocolate Chip Cookies. This recipe from A Pretty Life in the Suburbs only uses 1/2 c. sweetened condensed milk and is a great way to use up your leftover can from the peanut butter oatmeal bars.
• Sweetened Condensed Milk Snowballs. Another great recipe that uses only 1/2 c. sweetened condensed milk from Lord Byron’s Kitchen.

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