Preheat the oven to 180C/gas 4. Toss the berries, orange zest and a squeeze of juice, vanilla seeds, sugar and cornflour in a large bowl. Spoon into small, ovenproof dishes. For the crumble, mix sugar, buckwheat and ground almonds in a bowl. Use your fingers to rub in the butter, until large crumbs form. Sprinkle the fruit with the crumble and bake for 30 mins.