Preheat the oven to 180C/160C fan/Gas Mark 4. Grease and line a 23cm square cake tin with baking parchment

Put all of the pastry ingredients in a food processor or in a big bowl. Blitz or mix with a fork until the ingredients come together. Tip the dough out onto a floured work surface and bring together by hand. Knead for 2 minutes, just long enough to bring the dough together. Wrap in clingfilm and leave to rest in the fridge for 20 minutes.

To make the crumble topping, sift the flour into a large bowl Add the butter and icing sugar. Using your fingers, rub the butter into the flour and sugar to make a crumb-like mixture, then set to one side.

On a floured work surface, lightly roll out the pastry to about 5mm thick and press it into the bottom of the lined tin. Prick the pastry lightly with a fork and place in the oven to bake for 15 minutes.

Remove the tin from the oven. Layer the blueberries or bilberries over the pastry. Scatter over the grated marzipan and the crumble topping. Bake for 20 minutes until lightly golden brown on top. Leave to cool in the tin, then cut into squares.