Drain the cherries, reserving 7 tablespoons of the juice. Put a little of the reserved juice in a small saucepan with the cornflour and blend until smooth. Add the remaining juice and bring to the boil, stirring. Add the cherries and cook, stirring, for about 1 minute or until thickened slightly. Leave to cool.
Put the flour and mixed spice in a bowl or food processor. Add the butter and rub in with fingertips or process until the mixture resembles breadcrumbs. Add the sugar and ground almonds and mix or blend again until the mixture resembles a coarse crumble. Reserve 200 g (7 oz) of the mixture. Add the egg to the remaining mixture and mix to a soft dough.
Turn the dough into a greased 22–23 cm (8½–9 inch) square shallow baking tin and press it into the corners and slightly up the sides. Spread over the cherries to 1.5 cm (¾ inch) from the edges, then sprinkle with the reserved crumble mixture.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for about 1 hour until the crumble is golden. Leave to cool in the tin, then cut into squares.