To make hazelnut pastry; process nuts until fine. Add flour, sugar and butter; process until crumbly. With motor operating, add egg yolk and enough of the water so that ingredients just come together. Wrap pastry in plastic wrap; refrigerate for 30 minutes.
Grease 24cm round loose-based fluted flan pan. Roll pastry between sheets of baking paper until large enough to line flan pan. Lift pastry into pan, press into base and side; trim excess pastry. Prick base all over with a fork. Refrigerate for 30 minutes.
Preheat oven to 180°C (160°C fan-forced).
Place pan on an oven tray; line pastry with baking paper, fill with dried beans or rice. Bake for 15 minutes. Remove paper and beans; bake for a further 15 minutes or until browned lightly. Cool.
Meanwhile, combine frozen raspberries, sugar and juice in a small saucepan; stir over medium heat, without boiling, until sugar dissolves. Bring to the boil. Reduce heat; simmer, uncovered, stirring occasionally, for about 25 minutes or until thick. Cool. Spread cold berry mixture into pastry case.
Place chopped chocolate, butter, cream and liqueur into a medium heatproof bowl; stir over a medium saucepan of simmering water until smooth (don't let water touch base of bowl). Pour mixture into pastry case. Refrigerate tart for 2 hours or until firm.
Soften the smooth side of the extra chocolate slightly by holding your hand on the surface for about a minute; carefully drag a cheese slicer, or large sharp knife, across the back of the chocolate to make curls.
Serve tart topped with fresh raspberries and chocolate curls.