Sift together the flour and 25 g (1 oz) icing sugar. Rub in the butter. Add the egg yolk and bind to a smooth paste adding 15 ml (1 tbsp) water if necessary. Chill for 20 minutes then use the mixture to line eight boat moulds about 11.5 cm (4 1/2 inches) in length.

Spread the hazelnuts out on a baking sheet and brown in the oven at 180°C (350°F) mark 4 for 15 - 20 minutes. Allow to cool, then finely chop, leaving the skins on. Mix with the ground almonds.

Lightly beat one egg white with the caster sugar until frothy. Beat in the nut mixture together with the water.

Spoon a little of the mixture into each lined mould. Bake at 190°C (375°F) mark 5 for 15 - 20 minutes.

For the frosting: sift the remaining icing sugar and beat with just enough egg white to give a coating consistency. Thinly coat each of the barquettes with the icing.

Return to the oven for about 5 minutes, or until a pale golden colour.