Plum raspberry crumble bars

These deliciously fruity bars are perfect with a flask of tea on a crisp, autumn walk

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190g plain flour 140g light brown soft sugar 165g cold salted butter, cut into cubes 150g jumbo oats 50g pecans roughly chopped (optional) 150g raspberries 4tbsp raspberry jam squeeze of lemon juice 2 plums, roughly chopped