Creating the delightful Mixed Berry Crisp is simple when you follow these steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C).
2. Prepare the Berry Mixture: In a large bowl, combine the mixed berries, granulated sugar, lemon juice, cornstarch, and vanilla extract. Gently toss until the berries are well coated.
3. Transfer to Baking Dish: Pour the berry mixture into a greased 9×13-inch baking dish, spreading it evenly across the bottom.
4. Make the Topping: In another bowl, mix the rolled oats, flour, brown sugar, melted butter, cinnamon, and salt together until crumbly.
5. Add Topping: Spread the oat mixture evenly over the berry layer in the baking dish.
6. Bake: Place the dish in the preheated oven and bake for 30-35 minutes or until the topping is golden brown and the berries are bubbling.
7. Cool Down: Remove from the oven and let it cool for about 10 minutes before serving. This allows the juices to thicken slightly.
8. Serve Warm: For an indulgent touch, serve while still warm with a scoop of vanilla ice cream or a dollop of whipped cream.

By adhering to these straightforward steps, you can achieve a delicious Mixed Berry Crisp ready to impress.