This apple blueberry crisp combines two of my favorite fruit desserts in the confines of a single pan. Tart apples and jammy berries are topped with a buttery oat topping for an unexpected dessert that you'll turn to again and again. It comes together quickly, and it works with both fresh and frozen fruit. Serve it warm with a scoop of vanilla ice cream.
Place the apples and blueberries in a large bowl. In a small bowl, whisk the granulated sugar, brown sugar, cornstarch, cinnamon, and salt.
Add the lemon juice and zest, then add the sugar mixture to the fruit and toss to coat.
Transfer the mixture to the prepared pan.
Place the butter, flour, sugar, cinnamon, and salt in a food processor. Pulse until the mixture comes together but isn't fully combined. Stir in the oats and nuts.
Crumble the mixture over the fruit.
Bake for 35 to 40 minutes, until the topping is browned, the filling is bubbling around the edges, and the apples are fork-tender. If the top browns too quickly, tent with foil.
Rest for 20 to 30 minutes before serving so the filling can set.