If you’ve got some rhubarb lying around and no idea what to do with it—this one’s for you.
These Rhubarb Oatmeal Cookie Bars are sweet, a little tart, and seriously cozy.
Think soft cookie on the bottom, gooey rhubarb jam in the middle, and a buttery oatmeal crumble on top.
Pure magic. I love making this when rhubarb’s in season and I want something that’s not fussy but still feels special.
Why I Love This Recipe
Honestly, I’ve made this recipe more times than I can count—especially when I get a big bundle of rhubarb from the farmers’ market. Here’s why it hits every time:
- Simple ingredients – Nothing fancy, just pantry staples and fresh rhubarb.
- Perfect balance – Sweet, tart, buttery, chewy, and crunchy all in one bite.
- No mixer needed – Just a bowl and a spoon.
- Freezer-friendly – Freeze leftovers for later and they still taste amazing.
This recipe is the definition of comfort food with a little spring twist.
Makes: 12 bars
Time: 50 minutes
🍓 What You’ll Need
For the rhubarb filling:
- 2 ½ cups rhubarb, diced
- ½ cup granulated sugar
- 1 tbsp lemon juice
- 1 tbsp cornstarch
For the base & topping:
- 1 ½ cups rolled oats
- 1 ¼ cups all-purpose flour
- ½ cup light brown sugar, packed
- ¼ cup granulated sugar
- ½ tsp baking soda
- ¼ tsp salt
- ¾ cup unsalted butter, melted
- 1 tsp vanilla extract
🧑🍳 Pro Tips
- Chop rhubarb evenly so it cooks down at the same rate—think small dice, like blueberry size.
- Don’t skip the lemon juice—it brightens up the flavor big time.
- Use rolled oats, not quick oats—they give a better texture in the crumble.
- Press the base firmly into the pan so it holds together when slicing.
- Let it cool fully before cutting or the bars will fall apart.
🛠 Tools You’ll Need
- 8×8-inch baking dish
- Mixing bowls
- Saucepan
- Silicone spatula
- Whisk
- Measuring cups and spoons
- Parchment paper
🔁 Substitutions & Variations
- Swap rhubarb for chopped strawberries or cherries.
- Make it gluten-free by using 1:1 gluten-free flour.
- Add cinnamon or ginger to the crumble for extra warmth.
- Vegan version? Use vegan butter or coconut oil.
⏱ Make-Ahead Tips
Make the rhubarb filling up to 2 days ahead. Store in the fridge and let it come to room temp before using. You can also bake the bars and freeze them for up to 3 months.
🍽️ Step-by-Step Instructions
Step 1: Make the rhubarb filling
Add diced rhubarb, granulated sugar, lemon juice, and cornstarch to a small saucepan. Cook over medium heat, stirring often, until it turns into a thick jam-like mixture (about 10–12 minutes).
Step 2: Mix the dry ingredients
In a large bowl, combine oats, flour, brown sugar, white sugar, baking soda, and salt.
Step 3: Add wet ingredients to make crumble
Pour melted butter and vanilla into the bowl. Mix until the dry ingredients are fully moistened and crumbly.
Step 4: Press base into pan
Line your 8×8 pan with parchment. Press two-thirds of the oat mixture firmly into the bottom.
Step 5: Add the rhubarb filling
Spread the cooled rhubarb filling evenly over the base.
Step 6: Add the crumble topping
Crumble the remaining oat mixture on top of the rhubarb layer. Don’t press it down.
Step 7: Bake it!
Bake at 350°F (175°C) for 30–35 minutes or until golden brown and bubbly around the edges.
🧊 Leftovers & Storage
Let the bars cool completely, then store in an airtight container:
- Room temp: 2–3 days
- Fridge: Up to 5 days
- Freezer: Up to 3 months. Wrap individually for easy grab-and-go!
🔬 Why This Recipe Works (Quick Science)
- Rhubarb releases water when it cooks. The cornstarch thickens that juice into a jammy layer.
- The butter in the oat mix melts, then solidifies while baking to bind everything together.
- Rolled oats hold their shape and texture during baking, making the perfect crumb.
⚠️ Common Mistakes
- Not cooking the filling long enough – You need it thick, not watery.
- Skipping parchment paper – These bars will stick without it.
- Cutting too soon – Let them cool or they’ll fall apart!
🍽 What to Serve With
- A scoop of vanilla ice cream
- Whipped cream
- Hot coffee or cold brew
- A glass of milk or oat milk
❓ FAQ
Q: Can I use frozen rhubarb?
Yes! Just thaw and drain off extra water first.
Q: Can I double this recipe?
Totally—use a 9×13 pan and add about 10 minutes to the baking time.
Q: Is it okay to use quick oats?
You can, but the texture will be softer and less chewy.
❤️ Final Thoughts
These Rhubarb Oatmeal Cookie Bars are the kind of dessert that feels like a hug. They’re simple, cozy, and always a crowd-pleaser. If you give them a try, I’d love to hear how it went! Drop a comment, share your twist on the recipe, or ask me anything. Let’s bake something good together. 💬👇
