Rhubarb season is notoriously short. Those beautiful, tart, ruby-red stalks usually peak in late spring and vanish from farmers’ markets before summer even officially begins. Luckily, rhubarb freezes exceptionally well, meaning you can preserve the harvest and enjoy your favorite treats all year long. And there is arguably no better way to use your freezer stash than by baking this Classic Rhubarb Crisp with Frozen Rhubarb.
This recipe celebrates the unadulterated, tangy flavor of the fruit (well, technically vegetable!) without masking it with strawberries or other heavy mix ins. The bottom layer is a thick, jammy, sweet and sour fruit filling that bubbles up around the edges of the pan. The top layer is a thick, golden brown blanket of buttery, cinnamon spiced oat crumble that provides the ultimate textural contrast.
If you adore the unique flavor of this tart spring staple whether it’s tucked inside flaky Baked Rhubarb Fritters or layered beautifully in these decadent Rhubarb Cheesecake Bombs this comforting, traditional crisp is guaranteed to hit the spot.
Why You Will Love This Dessert
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Bake Straight from Frozen: There is no need to remember to thaw your fruit! Thawing rhubarb can actually make it sad and mushy. This recipe allows you to toss the frozen chunks straight into the baking dish, saving you time and hassle.
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Perfect Flavor Balance: Rhubarb is incredibly tart on its own. By tossing it with sugar and topping it with a rich brown sugar crumble, you achieve a dessert that is perfectly balanced and not overly cloying.
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Pantry Friendly Topping: The crisp topping utilizes absolute basics: flour, oats, butter, sugar, and cinnamon. You probably have everything you need sitting in your cupboards right now.
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The Ultimate Comfort Food: Served warm right out of the oven with a melting scoop of vanilla bean ice cream, this crisp is the definition of a cozy, nostalgic dessert.
The Essential Ingredients
To ensure your frozen rhubarb bakes up thick and jammy instead of watery, you need the right ratio of thickeners and sugars!
For the Tart Rhubarb Filling:
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Frozen Rhubarb (5 cups): Keep it completely frozen! If you happen to have fresh rhubarb, you can use that too just reduce the baking time by about 5 to 10 minutes.
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Granulated Sugar (¾ cup): Essential for cutting the intense sourness of the raw rhubarb.
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Cornstarch (3 tbsp): This is the secret to baking with frozen fruit. As the frozen rhubarb bakes and releases extra water, the cornstarch absorbs the liquid, turning it into a thick, glossy syrup.
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Vanilla Extract (1 tsp): Adds a beautiful, aromatic depth to the fruit filling.
For the Buttery Oat Crumble:
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Old Fashioned Rolled Oats (1 cup): Provides that signature chewy, hearty crunch. Do not use quick oats, as they will turn to mush in the oven.
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All Purpose Flour (1 cup): Binds the topping together.
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Brown Sugar (1 cup): Light or dark brown sugar works wonderfully to provide a deep, caramel like sweetness that pairs beautifully with the cinnamon.
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Ground Cinnamon (1 tsp) & Salt (½ tsp): Warm spices and salt enhance the buttery flavor of the crust.
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Cold Unsalted Butter (½ cup / 1 stick): Must be very cold and cut into small cubes. This creates the crispy, crumbly texture we all love!
Hosting a big weekend dinner? Serve this crisp for dessert after a savory, protein packed main course like our Quick Healthy High-Protein Honey Garlic Shrimp or a comforting Ultimate Cheesy Ground Beef Melt!
Step-by-Step Instructions: Crispy Perfection
The beauty of a fruit crisp is that it is supposed to look rustic and messy. You do not need perfect pastry skills to nail this dish!
1. Prep the Oven and Pan Preheat your oven to 375°F (190°C). Generously grease a 9×9 inch square baking dish (or a similar sized deep pie dish) with non stick cooking spray or a pat of butter.
2. Toss the Frozen Filling In a large mixing bowl, add your completely frozen chopped rhubarb. Sprinkle the granulated sugar and cornstarch directly over the frozen fruit, then add the vanilla extract. Toss everything together vigorously until the rhubarb chunks are completely coated in the sugar and starch. Pour this mixture into your prepared baking dish, spreading it out into an even layer.
3. Build the Crumble Topping In a separate mixing bowl, combine the rolled oats, all purpose flour, brown sugar, cinnamon, and salt. Toss in your cold, cubed butter. Using a pastry blender, a fork, or your clean fingers, cut the butter into the dry ingredients until the mixture resembles coarse, wet sand with some larger, pea sized clumps remaining.
Need some fantastic side dishes for your gathering? Pair your dinner with a zesty Classic Pasta Salad and a savory Green Pea Salad with Bacon and Cheese!
4. Assemble and Bake Sprinkle the oat crumble evenly over the rhubarb filling in the baking dish. Do not pack it down tightly; keep it loose so the fruit juices can bubble up through the crust! Bake the crisp uncovered for 45 to 55 minutes. You will know it is done when the oat topping is deeply golden brown and the fruit filling is bubbling thickly around the edges.
5. Cool and Serve This is the hardest part: let the crisp cool on a wire rack for at least 15 to 20 minutes before serving. The filling needs this time to cool slightly so the cornstarch can set up. If you scoop it immediately, the juices will be runny! Serve warm with a generous scoop of vanilla ice cream.
Classic Rhubarb Crisp with Frozen Rhubarb
Ingredients
- 5 cups frozen rhubarb, chopped do not thaw
- ¾ cup granulated sugar
- 3 tbsp cornstarch
- 1 tsp vanilla extract
- 1 cup old-fashioned rolled oats
- 1 cup all-purpose flour
- 1 cup brown sugar, packed
- 1 tsp ground cinnamon
- ½ tsp salt
- ½ cup unsalted butter, cold and cut into cubes
Instructions
- Preheat oven to 375°F (190°C). Lightly grease a 9x9-inch square baking dish with butter or non-stick spray.
- In a large mixing bowl, combine the frozen rhubarb, granulated sugar, cornstarch, and vanilla extract. Toss well until evenly coated, then pour into the prepared baking dish.
- In a separate bowl, mix the oats, flour, brown sugar, cinnamon, and salt.
- Add the cold butter and cut it into the dry ingredients using a pastry blender or your fingers until the mixture resembles coarse crumbs with some pea-sized clumps.
- Sprinkle the crumble topping evenly over the rhubarb filling without pressing it down.
- Bake uncovered for 45 to 55 minutes, until the topping is golden brown and the filling is bubbling around the edges.
- Let the crisp cool for 15-20 minutes before serving to allow the filling to thicken.
Notes
Creative Customizations
While this recipe is a classic, you can easily customize it to fit your pantry:
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The Strawberry Twist: If you find pure rhubarb too tart, swap out 2 cups of the frozen rhubarb for 2 cups of frozen sliced strawberries.
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Nutty Crunch: Add ½ cup of chopped pecans, walnuts, or sliced almonds to the oat crumble for an incredible textural upgrade.
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A Tropical Alternative: Looking for a different kind of fruit dessert for the summer heat? Keep the oven off and whip up this creamy, no bake Hawaiian Cheesecake Salad instead!
Storage and Reheating Tips
If you are lucky enough to have leftovers, let the crisp cool to room temperature. Cover the baking dish tightly with plastic wrap or aluminum foil and store it in the refrigerator for up to 4 days.
To restore that incredible crunchy topping, reheat individual portions in the oven or air fryer at 350°F for about 5 to 7 minutes until warmed through. The microwave works in a pinch, but the oat topping will be much softer!
Pro Tip: Have leftover crisp in the morning? It makes an incredible, indulgent breakfast alongside a hot cup of coffee, or you can serve it next to a savory, protein heavy morning spread like these Twice Baked Loaded Breakfast Potatoes!