Pre-heat the oven to 200C.
Combine the flour, ground almonds (if using), and butter in a food processor or large bowl, and pulse briefly, or rub with your fingertips, until the mixture resembles very coarse breadcrumbs with a few larger lumps.
Add the sugars and stir through.
Sprinkle with a little cold water and rake through with a fork until you have a lumpy, crumbly mixture.
Put this in the freezer for 10 minutes, or if making ahead, in the fridge until you're ready to bake.
Meanwhile, put your prepared fruit in a lightly greased, shallow baking dish, and sprinkle with sugar – taste it first to see how much you think it needs.
You can also add any spices at this point (½ tsp ground cinnamon or ginger, for example, for apples or plums).
Arrange the crumble over the top of the fruit – don't press it down – and sprinkle with oats or nuts if using.
Bake for about half an hour, until golden and bubbling, and serve slightly cooled.
