Preheat the oven to 200°C.
Pulse flours and butter in a processor until they resemble breadcrumbs then blend in the egg.
Roll the pastry on a floured surface and line a 23cm tart tin.
Prick the base and chill the pastry in the fridge for 30 minutes.
Blind bake the case with parchment and beans for 25 minutes then without beans for 10 minutes.
Reduce the oven temperature to 180°C.
Sauté softened leeks in butter over low heat then set aside.
Whisk eggs with crème fraîche, salt, pepper, and brown crab meat.
Scatter leeks and white crab meat into the case and pour over the egg mixture.
Sprinkle with cheese and bake for 25 minutes until golden and just set.
Cool the tart in the tin for 15 minutes before serving.