Method

• 1.
  To make pastry, place butter and 1/4 cup (55g) sugar in a stand mixer with paddle attachment and beat until smooth. Beat in whole egg. Fold in flour, baking powder and shape into a disc. Enclose in plastic wrap and chill for 2 hours. Preheat oven to 200°C. Roll out pastry between 2 sheets of baking paper to 3mm thick. Use to line the base and side of a 22cm x 5cm loose-bottomed, fluted tart pan, trimming any excess, then freeze for 10 minutes. Line pastry with baking paper and pastry weights. Place on a baking tray and bake for 20 minutes or until edges are light golden. Remove weights and paper, and bake for a further 15 minutes or until base is golden and dry. Remove from oven and cool slightly.
• 2.
  To make filling, melt chocolate in a heatproof bowl set over a saucepan of gently simmering water. Stir occasionally until melted. Cool slightly, then beat in egg yolks (it may look seized at this point but will come back together when cream is added). Cool to room temperature. Beat in whipped cream in 2 batches. Pour mousse into tart shell, chill for 4 hours or until firm.

• 3.
  To make coffee meringue, place egg whites, instant coffee, cream of tartar and remaining 11/2 cups (330g) sugar in a heatproof stand mixer bowl. Place over a saucepan of gently simmering water and stir with a whisk until sugar dissolves and egg mixture is hot. Remove from heat. Whisk to stiff peaks until cool. Spoon over mousse and use a blowtorch to caramelise top of meringue. Serve immediately.