Method
1. Pre-heat oven - 190 °C / 375°F
2. Line a baking tray measuring approx 13"x7" with baking parchment and put to one side
3. Add all purpose flour and baking powder to a clean large mixing bowl
4. Rub the butter into the flour using your fingertips until the mix resembles breadcrumbs
5. Add in the white and brown sugar, the salt, egg and vanilla extract, then give it a mix with your hands
6. Take approx. half of this mixture and place it into your prepared baking tray
7. Flatten the mixture down and squash it to the edges and corners
8. Take a medium sized bowl and add your strawberries, blueberries, sugar, lemon juice and cornstarch
9. Mix together gently and then layer this mixture on top of your crumble base
10. Sprinkle the remaining crumble mixture on top of the blueberries
11. Place in the oven to cook for 40 minutes - until the topping looks golden brown
12. Take out of the oven and leave to cool in the tin
13. Gently slide (baking parchment too) onto a cutting board and let cool completely
14. Once cool, slide out of the baking parchment and cut into 24 bars
15. Whilst the streusel bake is cooling, make the white chocolate custard dip:
Place the egg yolks, sugar and cornflour in a large bowl or jug and whisk. Put to one side
16. Place the cream, milk and vanilla extract in a pan, and heat until it’s just about to boil
17. Turn off the heat and pour a splash of the hot milk mixture into the egg mixture whilst whisking with a hand whisk
18. Continue to add the milk a little at a time whilst whisking, then pour the whole mixture back in the pan
19. Stir slowly with the whisk whilst heating on a medium heat
20. Once the custard has thickened, turn off the heat and stir in the butter
21. Place the chopped chocolate in the pan and leave for a minute or two to melt, then stir to fully incorporate
22. The custard can be served warm right away, or can be left to cool with a layer of plastic wrap on top
23. Serve the sliced streusel bars with little individual dishes of the white chocolate custard dip