Combine rhubarb, cherries, sugar, cornstarch, and kirsch in a large bowl, and toss to coat. Pour the fruit mixture into an 8x8 square pan.
In a medium bowl, combine the flour, oats, brown sugar, butter, nutmeg, and salt. Using a spatula (or your fingers), bring the mixture together into a loose crumble. Sprinkle the crumble topping evenly over the fruit.
Bake until the filling it hot and bubbling and the topping is crisp and golden brown, about 30 minutes. Serve warm with vanilla ice cream.
Notes
We made this with fresh sour cherries, which are incredible, but have a very short season. You can substitute frozen sour cherries if you can’t find fresh ones.
Recipe by Three Many Cooks at https://threemanycooks.com/recipes/sweet-treats/sour-cherry-rhubarb-crisp/