1. Prepare streusel topping. In large bowl, combine flour and butter. Use an electric mixer on low speed and blend until butter pieces are pea-size. Alternately, use a pastry blender or fork.
2. Add brown sugar, oats, salt, and cinnamon if using; mix until thoroughly combined and the mixture loses any signs of dry flour streaks and begins to clump slightly. Set aside.
3. Prepare fruit filling. Preheat oven to 350 degrees F. Spray a 9-by-13-inch baking dish with vegetable cooking spray.
4. Place peaches and plums in large mixing bowl. Sprinkle both sugars, lemon juice, flour, and cinnamon over fruit. Toss together gently with a large spoon. Transfer fruit to prepared pan.
5. Sprinkle reserved streusel over top of fruit mixture, covering fruit well. Bake until filling is bubbling all around the dish and liquid looks thickened, about 45 to 60 minutes depending on depth of fruit mixture.
6. Cool pan on a wire rack for 10 to 15 minutes before serving so the filling can settle. Serve warm with ice cream or whipped cream if desired.
Source: Hannaford fresh Magazine, July - August 2013