Preheat the oven to 400ºF. Melt the butter and put to one side for a mo.
Combine the oats, flour, brown sugar, almonds, kernels, and cinnamon in a bowl. Tip the blackberries into a wide shallow baking dish (I used one here with a 3-cup capacity), sprinkle over the vanilla sugar and cornstarch, and tumble about to mix.
Stir the melted butter into the crisp topping and spoon on top of the blackberries to cover but not absolutely thoroughly. Bake for 25 minutes and serve with ice cream or heavy cream.