Replace the flour in the apple filling with 1 ½ tablespoons arrowroot powder or cornstarch. 2. Replace the all-purpose flour in the crisp topping with a gluten-free all-purpose flour blend that contains xanthan gum in the ingredients. We typically use King Arthur’s Gluten-Free Measure-for-Measure Flour or Bob’s Red Mill 1:1 Gluten-Free Baking Flour (affiliate links). 3. Use certified gluten-free rolled oats. While we enjoyed this gluten-free version, it doesn’t deliver the same exact crisp topping texture, so if you can tolerate gluten, I recommend making the original version.