Preheat oven to 220°C/425°F. Grease six holes of a 12-hole (⅓ cup/80ml) muffin pan. 2 Combine egg yolks, caster sugar, cornflour and cocoa in a medium saucepan; whisk in milk and cream until smooth. Stir over medium heat until mixture boils and thickens; transfer to a heatproof bowl, cover surface with plastic wrap. Cool. 3 Meanwhile, cut pastry sheet in half; stack two halves, press firmly. Roll pastry up tightly from short side; cut log into six slices. Roll slices between sheets of baking paper into 12cm (4¾-inch) rounds; press rounds into pan holes. 4 Pour custard into pastry cases; bake about 20 minutes or until set. Cool in pan. 5 Serve tarts topped with berries; dust with sifted icing sugar.