For the topping:
1. Preheat the oven to 350°F. Mix together the blueberries, honey, lemon zest and juice,
and vanilla pod and seeds and pour into a baking dish roughly 10 x 6 inches. Set aside.
2. For the topping, rub the butter into the flour and sugar until it resembles breadcrumbs
(alternatively, do this in a food-processor). Stir in the oats and cornflakes. Scatter all over the top of the blueberry mixture and bake for 30–35 minutes, or until golden brown all over and bubbling underneath.
3. Serve with ice cream, custard, Greek yogurt or heavy cream, if you wish.