Make pastry: Process flour, sugar and butter until crumbly. Add egg yolk and enough of the water, processing until ingredients come together. Knead dough on a floured surface until smooth. Enclose pastry in plastic wrap; refrigerate for 30 minutes.

Grease a 24cm round loose-based fluted flan pan. Roll pastry between sheets of baking paper until large enough to line pan. Ease pastry into pan, press into base and side; trim edge. Cover; refrigerate for 30 minutes.

Preheat oven to 180°C.

Place pan on an oven tray. Line pastry case with baking paper; fill with dried beans or rice. Bake for 15 minutes. Remove paper and beans; bake for 15 minutes or until browned lightly. Cool.

Place nuts on an oven tray; roast for 5 minutes or until browned lightly, cool. Place nuts in a tea towel; rub to remove skins. Place nuts in pastry case.

Combine sugar, butter, extract and ⅔ cup cream in a small saucepan; bring to the boil. Reduce heat; simmer, uncovered, for 8 minutes or until golden and thickened. Pour caramel over nuts; cool until filling is firm.

Place chocolate in a small heatproof bowl. Bring remaining cream to the boil in a small saucepan. Pour hot cream over chocolate; stir until smooth. Spread chocolate mixture over pie. Refrigerate for 3 hours or overnight. Remove pie from refrigerator 30 minutes before serving.