Rhubarb Oatmeal Bars

Rhubarb Oatmeal Bars are sweet and tart, gooey and crispy, with an almond coconut crumble topping. An easy cookie bar recipe that starts with cookie mix. Use fresh or frozen rhubarb to get the flavors of spring anytime of year.

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You’re going to love these

So. Easy. These rhubarb oat bars are so easy to stir together in about 10 minutes, then sit back and wait for your kitchen to smell amazing. 

Cookie bars from cookie mix. Looking for an extra hand in the kitchen? Get a little help from a pouch of cookie mix, then dress it up with your own special touches. These rhubarb bars start with oatmeal cookie mix and some delicious stir-ins that make it taste like homemade. 

Fresh or frozen rhubarb. You can use either fresh or frozen rhubarb in these oatmeal bars. So if you have a stash of rhubarb in your freezer, you can get a taste of spring even in the dead of winter.

Crumble bars. The topping of these oatmeal bars is made from oatmeal cookie mix, cinnamon, almonds, and coconut — so it creates a crunchy topping with lots of texture and nutty flavors. Kind of like a rhubarb crumble or crisp. 

Sweet and tart. A lot of times, rhubarb is paired with strawberries because rhubarb on its own can be a bit too tart. But tossing the rhubarb in sugar and layering it in between an oatmeal cookie crust and crumbly coconut almond topping provides plenty of sweetness. But, if you feel strawberries are missing, go ahead and substitute part of the rhubarb for strawberries. 

Ingredient Notes & Substitutions

Oatmeal cookie mix. I chose oatmeal cookie mix because I wanted to create a rhubarb bar that was like rhubarb crisp or a rhubarb crumble bar. But, you can use any kind of cookie mix you love, like sugar cookie mix, snickerdoodle cookie mix, or white chocolate macadamia nut cookie mix. 

Butter. You need room temperature butter for these oatmeal rhubarb bars so you can get the cookie mix ingredients to fully incorporate into a soft dough. I always forget to soften my butter until right before I start baking. So, if you’re like me, you can use one of these tricks to get soft butter quickly. 

Fill a glass measuring cup with water and microwave it on high for 2-3 minutes. While that’s happening, cut a cold stick of butter into ½” thick slices and arrange them in a single layer on a small plate. When the water is hot, QUICKLY open the microwave and place your plate of butter inside (keep the water in the microwave). In 10 minutes, you’ll have softened butter. 

Other clever ways of softening butter include grating it with a box grater, placing it in a zipper bag and whacking it with a rolling pin to flatten it out so it will quickly get to room temperature, or placing it in a metal bowl over a water bath. 

Eggs. When baking these rhubarb bars, I always use room temperature eggs. And since I usually forget to set them out ahead of time, I just place them in a bowl of warm water for about ten minutes, and they’re ready. 

Almonds. You can use whatever kind of nut you like in the crumble topping for these rhubarb bars. Walnuts, pecans, hazelnuts, macadamia nuts — or a combination of all of them! 

Coconut. I didn’t realize coconut was a divisive ingredient. I just thought everyone loved it as much as I do. So if you’re not a lover of coconut, go ahead and add a second kind of nut or seeds like sunflower or pumpkin. Or even pretzels (what?). 

Cinnamon. The oatmeal cookie mix already has some cinnamon in it, but I wanted more. So I added more. If you want to add some different flavor dimensions, you can add some pumpkin pie spice or apple pie spice. 

How to bake with frozen rhubarb

I made these rhubarb oatmeal bars when rhubarb wasn’t in season, so I had to use frozen. Using frozen rhubarb without defrosting it first will add too much water to the recipe, so I defrosted it first. But measuring frozen vs. fresh can be a bit tricky because frozen fruit takes up more room in the measuring cup. I measured out an extra cup — so I had 3 cups of frozen rhubarb. After I defrosted and drained it, I had 2 cups of rhubarb,which was exactly what I needed to completely cover the crust. 

How to make rhubarb oatmeal bars

Preheat the oven to 350. Spray the bottom of a 9x13 pan. 

With a mixer, combine the cookie mix, softened butter, water, and egg until it forms a soft dough. Pat ⅔ of the oatmeal cookie mix into the pan and bake it for 15 minutes. 

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To the remaining ⅓ of the cookie mix, add the cinnamon, coconut, and almonds. Combine until all ingredients are incorporated. 

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Toss the rhubarb with ½ cup sugar and ¼ cup of flour. 

Evenly spread the rhubarb mixture over the cookie crust layer. 

Crumble the cookie, almond, and coconut mixture over the rhubarb. 

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Bake for 25-35 minutes or until the crumble is golden brown or the internal temperature reaches 165-200. 

Let cool for 20 minutes and enjoy a warm rhubarb oatmeal bar with a scoop of vanilla ice cream or a dollop of whipped cream. Or let them cool completely. 

These rhubarb oatmeal bars will be crumblier during the first day and soften over time because of the fruit filling. So if you prefer a crispier texture, bake these the same day you serve them. The next day, the rhubarb filling will still be gooey and the cookie crust and crumble topping will be soft and delicious.

Recipe Essentials

Pyrex Bakeware

These Pyrex baking dishes are awesome. They have really large handles, so you can grab them out of the oven with your oven mitt on -- without putting your thumb in your freshly baked creation. Also, the lids snap on nice and tight.

KitchenAid 7-Speed Hand Mixer

I haven't yet invested in a stand mixer because this hand mixer has held up to everything I've thrown at it. Plus, it's easy to clean and stash away.