Raspberry-Rhubarb Crumble

"The Ingredients Filling: 3 cups fresh raspberries 3 cups rhubarb, chopped Zest and juice from ½ lemon ? cup sugar 1 tablespoon cornstarch Topping: ½ cup flour ½ cup old-fashioned oats ¼ cup light brown sugar ½ teaspoon ground cinnamon ½ teaspoon kosher salt 6 tablespoons cold unsalted butter, cut into cubes Vanilla ice cream, optional, for serving The Steps Preheat your oven to 375°F. Make the filling. In a large bowl, add raspberries, rhubarb, lemon zest and juice, sugar, and cornstarch. Toss to com..."