Cut the pastry into 6 pieces, then roll each piece out thinly on a lightly floured surface until a little larger than a buttered 10 cm (4 inch) individual fluted loose-bottomed tart tin. Press the pastry over the base and sides, then trim with scissors to a little above the top of the tin. Repeat until 6 tart cases have been made. Put on a baking sheet, prick the bases with a fork, then chill for 15 minutes. Bake the tarts blind (see
Melt the dark chocolate and butter in a bowl set over a saucepan of gently simmering water, making sure that the water does not touch the base of the bowl. Stir in the egg yolks, one by one, then take the bowl off the heat and stir in 6 tablespoons of the cream and the sugar.
Whisk the egg whites until they form soft peaks, then fold a tablespoon into the chocolate mixture to loosen it. Add the remaining egg whites and fold in gently. Pour into the baked tart cases and chill for 3 hours until set.
Melt the white chocolate in a bowl over hot water as above. Remove the tarts from the tins and transfer to serving plates. Whip the remaining cream until it forms soft swirls, fold in the white chocolate and liqueur, then spoon on to the tarts. Drizzle with the milk chocolate and leave to stand for 10 minutes before serving.