Preheat oven to 350°F and lightly grease an 8×8-inch baking dish.
In a large bowl, combine the rhubarb, strawberries, cornstarch, honey, and lemon juice. Stir until the fruit is evenly coated, then spread the mixture evenly in the prepared baking dish.
In a separate bowl, mix together the oats, almond flour, coconut sugar, cinnamon, and salt. Pour in the melted butter and stir until the mixture forms coarse crumbs.
Fold in the slivered almonds, then sprinkle the topping evenly over the fruit.
Bake for 35–40 minutes, or until the topping is golden brown and the fruit is bubbling around the edges.
Let cool for at least 10 minutes before serving. Serve warm, optionally with whipped cream or vanilla ice cream.
Balance the fruit: Rhubarb is very tart, so using more strawberries than rhubarb helps create a balanced sweet-tart flavor without needing extra sweetener.
Let the filling thicken: Cornstarch helps absorb excess moisture from the fruit as it bakes, preventing a watery or soupy crisp.
Mix topping until crumbly: The topping should resemble coarse crumbs before baking. This ensures it bakes up crisp rather than dense.
Don’t pack the topping: Sprinkle the topping loosely over the fruit to allow air circulation and even browning.
Bake until bubbling: The crisp is done when the fruit is bubbling around the edges and the topping is golden brown, this ensures the filling has thickened properly.
Rest before serving: Let the crisp cool for at least 10 minutes after baking so the juices can settle and the topping can firm up.