Roll the pastry out thinly on a lightly floured surface, then stamp out 24 × 6 cm (2½ inch) circles with a fluted biscuit cutter and press into the buttered sections of 2 × 12-section mini muffin tins. Reknead and reroll the pastry trimmings as needed. Prick the base of each tart 2–3 times with a fork, then chill for 15 minutes.
Line the tarts with small squares of nonstick baking paper and baking beans and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 5 minutes. Remove the paper and beans and cook for a further 4–5 minutes until the bases are crisp. Remove the cases from the tins and cool on a wire rack.
Melt the chocolate in a bowl over a saucepan of very gently simmering water, making sure that the base of the bowl does not touch the water. Stir until smooth.
Whip the cream until it forms soft swirls, then fold in the melted chocolate and chopped mint. Spoon into the cooled pastry cases and top each one with a raspberry and tiny mint leaf. Dust lightly with sifted icing sugar just before serving.