Preheat oven to Gas Mark 4, 190°C, fan 170°C. Line a 20cm (8in) tin with nonstick baking paper. Melt the butter and mix in the flour and sugar. Press into the tin to cover the bottom evenly. Bake for 15mins until golden.
Put the dried fruit, granulated sugar and 200ml (1⁄3pint) water into a pan and simmer for 10mins so the fruit plumps up.
Make the crumble. Rub together the butter and flour. Stir in the muscovado sugar and muesli.
Spoon the fruit onto the biscuit base and scatter over the crumble. Bake for 20-25mins until golden.
Cool in the tin, then cut into squares.