1. Fire up your Ooni pizza oven.
2. First, prepare the crumble topping.
3. Add a little olive oil to your Skillet and place inside your Ooni to warm up.
4. In a small bowl, add 4 tablespoons of boiling water to the cornflour and mix until well combined.
5. Once the Skillet is warm, remove it from the oven and add the apples.
6. Remove the Skillet and add the cornflour-water mixture, brown sugar, vanilla extract and maple syrup.
7. Top the fruit evenly with the crumble mixture and continue to cook for another 10 minutes, or until the topping is toasted and crunchy.
8. Remove Skillet from the oven and serve warm, topped with a scoop of vanilla ice cream.