Gluten-Free Rhubarb Crisp

Gluten-free rhubarb crisp is made by tossing chopped rhubarb with lemon juice, sugar, and cornstarch, then covering it with a buttery buckwheat oat topping.

Buckwheat flour has an earthy, slightly nutty flavour that works well with rhubarb, and when it’s mixed with rolled oats, brown sugar, cinnamon, and butter, it bakes into a tender, golden topping without needing a gluten-free flour blend.

Updated May 2026 with expanded notes and clearer instructions.

Gluten-free rhubarb crisp is a recipe I originally made because my father-in-law ate gluten-free for the last several years of his life.

I chose buckwheat flour because I find it has more flavour than many gluten-free flour blends. The topping is easy to mix by hand, so there’s no mixer needed and no fussy technique. The rhubarb filling is straightforward too, with lemon juice, sugar, and cornstarch to help it bake up thick and saucy. I love it served warm, with vanilla ice cream.

Ingredients for Gluten-Free Rhubarb Crisp

Ingredient Notes

• Buckwheat Flour: I use finely milled buckwheat flour, which is often greyish in colour and has an earthy, slightly nutty flavour
• Butter: I use salted butter for all of my recipes, and it should be at room temperature so it rubs easily into the topping.
• Cornstarch: Break up any lumps before adding to the rhubarb.
• Lemon Juice: I use freshly squeezed lemon juice for all of my recipes.
• Oats (Rolled): Use rolled oats, also called large flake oats, not quick oats or steel-cut oats. If you’re baking for someone with celiac disease, make sure the oats are certified gluten-free. Regular oats can come into contact with gluten-containing grains during growing, processing, or packaging.
• Rhubarb: Fresh or frozen rhubarb can be used, and the pieces should be chopped to about ½ inch so they soften evenly.
• Salt: I use table salt for all of my recipes.
• Sugar (Brown): Sometimes labelled old-fashioned brown sugar or dark brown sugar.

It’s important to note that when making substitutions in recipes, the texture and flavour may be slightly different. However, these substitutes are the best options for changing the original recipe.

Ingredient Substitutions

• Buckwheat Flour: Substitute with the same quantity of millet or oat flour. If gluten isn’t an issue, use regular all-purpose flour.
• Butter: Use the same amount of unsalted butter or margarine.
• Cinnamon (Ground): Swap the cinnamon for 1 teaspoon of apple pie spice or my homemade chai spice mix.
• Cornstarch: Use the same amount of arrowroot powder or tapioca starch.
• Lemon Juice: You can use the same amount of bottled lemon juice
• Oats (Rolled): Use ½ cup (50 g) of quick oats in place of the rolled oats, but note the texture will be different.
• Salt: Swap the table salt for fine sea salt.
• Sugar (Brown): Light brown sugar or golden-yellow sugar would be good substitutes.
• Sugar (Granulated): Use the same amount of cane sugar.

Recipe Variations for Gluten-Free Rhubarb Crisp

• Cardamom: ¼ teaspoon, ground, added to the buckwheat oat topping with the cinnamon
• Ginger (Fresh): 1 teaspoon, finely grated, stirred into the rhubarb filling with the lemon juice
• Nuts: ¼ cup (30 g), chopped almonds, hazelnuts, pecans, or walnuts, mixed into the topping after the butter is rubbed in or sprinkled over the crisp before baking
• Orange Zest: 1 ½ teaspoons to 1 tablespoon, finely grated, stirred into the rhubarb filling before transferring it to the baking dish
• Strawberries: 1 cup (150 g), sliced, used in place of 1 cup (150 g) of the rhubarb and mixed into the filling before adding the sugar and cornstarch

Use the JUMP TO RECIPE button at the top of this post, or scroll to the bottom to see the PRINTABLE recipe card with ingredient measurements and complete instructions.

How To Make Gluten-Free Rhubarb Crisp

STEP 1. Toss the chopped rhubarb with the lemon juice, sugar, and cornstarch until the pieces are evenly coated.

STEP 2. Mix the buckwheat flour, brown sugar, oats, cinnamon, and salt, then rub in the butter until no dry bits remain.

STEP 3. Spread the rhubarb in the prepared baking dish, then sprinkle the buckwheat oat topping evenly over the fruit.

STEP 4. Bake until the topping is golden and the rhubarb filling is bubbling around the edges.

Recipe Notes

• For detailed ingredient notes, substitution tips, variations, and step-by-step photos, scroll through the full recipe post.
• Use a digital kitchen scale for precise measurements and an oven thermometer to confirm your oven is heating correctly.
• To switch to gram measurements, click “Metric grams” in the ingredients section of the recipe card.
• I used an 8-inch (20-cm) square baking dish for this recipe. If using a 9-inch (23-cm) square dish, increase the rhubarb to 5 cups (750 g) and expect the topping to bake in a slightly thinner layer.
• Stir the rhubarb filling again before adding it to the baking dish, as the sugar and cornstarch can settle in the bottom of the bowl.

Storage for Gluten-Free Rhubarb Crisp

• Store leftover crisp covered in the refrigerator for up to 3 days. Reheat individual portions in the microwave, or warm in a 300ºF (150ºC) oven until heated through. The topping will soften after refrigeration, but warming it in the oven can help bring back some texture.