Rhubarb, cardamom and rye streusel

1. Preheat the oven to 200˚C, gas mark 6, and line a rectangular cake tin (about 28cm x 20cm) with baking parchment. Put the flour, sugar and a pinch of salt into a food processor. Add the 140g butter and whizz until the mixture resembles fine breadcrumbs. (Alternatively, rub the butter in by hand.) Transfer to a bowl and stir through the egg and 2 tbsp water. Knead gently just until it forms a dough. Press the dough into the lined tin to form a flat, even layer. Cover and chill for 20 minutes.

2 . eanwhile, make the topping. Grind the seeds from the cardamom pods, then combine in a bowl with the flours, caster sugar and a pinch of salt. Rub in the butter and bring together with 1 tbsp water to form a ball; set aside. In a medium bowl, combine the filling ingredients, then spread over the chilled dough base. Break the ball of streusel topping into pebble-sized pieces and crumble over the rhubarb, then scatter over the demerara sugar. Bake for 1 hour-1 hour 10 minutes, until the top is a deep golden brown.

3. Leave to cool completely (and preferably chill overnight). Don’t attempt to serve it while still hot as it will fall apart. Once cool, either serve at room temperature or reheat slightly and serve with yogurt, cream or ice cream, if liked.