Method

• 1.
  Grease a 23cm loose-bottomed fluted tart pan. For pastry, place flour, cocoa, icing sugar and 120g butter in a food processor and process until mixture resembles fine breadcrumbs. Add egg yolk and 2 tbs cold water, and process until mixture comes together in a smooth ball. Wrap in plastic wrap and chill for 30 minutes.
• 2.
  Roll out pastry on a lightly floured board then use to line the tart pan. Trim, then chill for a further 30 minutes.
• 3.
  Preheat oven to 180°C. Line pastry with baking paper, fill with pastry weights or uncooked rice and bake for 10 minutes. Remove paper and weights or rice, then bake for a further 5 minutes until just cooked.
• 4.
  While pastry is baking, place 450g cooking chocolate and remaining 120g butter in a heatproof bowl over a pan of simmering water (don’t let bowl touch water). Stir until smooth. Remove from heat and cool slightly. Add eggs, caster sugar, cream and vanilla. Stir until combined and sugar is dissolved.
• 5.
  Reduce the oven temperature to 170°C. Pour filling into the tart shell and bake for 15 minutes until just set, then cool.
• 6.
  Melt remaining chocolate in a bowl over a pan of simmering water (don’t let bowl touch water). Stir until smooth. Pour over tart, tilting to coat top. Top with truffles and serve with thick cream, if desired. Serves 8-10.