For the Blueberry pie filling:

1. Combine the blueberries, sugar, and orange juice into a medium saucepan over medium heat and bring to a boil.
2. Bring to boil for a minute. Mix the cornflour with 4 teaspoons of warm water.
3. Add the cornflour mixture to the blueberry mixture. Simmer on low heat for 4-5 minutes until the mixture has thickened. Remove from heat and set aside to cool.

For the Custard filling:

1. In a microwave-safe bowl add in the First Choice Custard and microwave for 2 minutes on high. Whisk the cornflour and First Choice Milk milk together separately until smooth.
2. Whisk cornflour mixture into the custard and microwave at 2-minute intervals until thick, ensuring to whisk the mixture in between.
3. Once thickened allow to cool for 15 minutes. Use your hands to lightly press cling wrap over the custard, so that it is touching the top of the custard and allow it to cool.

For the biscuit crumble base:

1. Preheat oven to 190°C. Line a 20×20 cm square baking pan with aluminium foil. Set aside.
2. Combine the flour, oats, sugar, baking powder, cinnamon, and salt in a large bowl and whisk. Add the melted First Choice Butter and mix until the mixture is crumbly.
3. Press 2/3 of the mixture into the prepared baking pan. Place in the oven for 10 minutes.
4. Remove crust from the oven after 10 minutes and spread the custard filling over, smoothen out using a spatula.
5. Top with the blueberry pie filling, ensuring to spread the filling out evenly. Top with the remaining crumble.
6. Bake for 35-40 minutes until the topping is lightly browned. Remove from the oven and allow to cool on a wire rack. Transfer to the refrigerator to chill for 3 hours before cutting into squares.