- Preheat oven to 375°F. Line large baking sheet with parchment paper.
- To make streusel, with your fingers, rub together 1/3 cup of flour and the butter in small bowl until small crumbs form. Stir in brown sugar, oats, oil, and cinnamon.
- Combine apples, cherries, granulated sugar, and remaining 1 tablespoon flour in large bowl and toss to coat. Unroll crust onto prepared baking sheet. Mound apple mixture on crust, leaving 1 1/2-inch border. Sprinkle streusel evenly over apple mixture. Fold rim of crust over to partially cover filling, pleating and pressing lightly.
- Bake until apples are tender when pierced with tip of small knife, 50–55 minutes. Cool 10 minutes on baking sheet on rack. Slide tart on parchment paper onto wire rack to cool completely.
- Per serving: 1/12 of tart
Use a variety of apples to give the crostata more complex flavor. Try any combination of Granny Smith, Golden Delicious, Pink Lady, Honeycrisp, Rome, or Cortland apples.