Blueberry Rhubarb Crisp With Pistachio-Oat Crumble

["1. Move oven rack to upper third of oven and preheat oven to 375 degrees. Prepare 2 quart baking dish by coating bottom and sides with non-stick spray or softened butter. In a medium bowl, stir together sugar and tapioca. Add in rhubarb and blueberries and toss to coat. Spread mixture in the bottom of prepared baking dish.", "", "2. In a medium bowl, combine flour, oats and sugars and whisk until well combined. Cut butter into 1/2"" pieces and blend butter with oat mixture by using your fingers to combine and crumble, until the mixture resembles a coarse meal. Add pistachios to oat mixture and stir until well combined.", "", "3. Take a small handful of topping and squeeze it into a compact chunk and crumble it over blueberry filling. Continue with remaining topping and crumble evenly over the filling until all of the crumble is used up.", "", "4. Bake in upper third of oven for about 45 minutes, or until the filling is bubbling and the topping is golden crisp. Serve immediately or at room temperature, topped with a dollop of fresh whipped cream or a small scoop of vanilla bean ice cream."]