40 gmsoft, unsalted butter55 gm(¼ cup) caster sugar1 tspvanilla extract1egg100 gm(2/3 cup) plain flour50 gmhazelnut meal1 tspbaking powderHazelnut praline75 gm(1/3 cup) caster sugar30 gmhazelnuts, roasted and peeledEspresso icing240 gm(1½ cups) pure icing sugar, sieved30 mlespresso coffee30 mlhazelnut liqueur15 gmbutter1vanilla bean, scraped seeds only or ½ tsp vanilla bean paste
For hazelnut praline, combine sugar and ¼ cup of water in a small saucepan and stir over medium-high heat until sugar dissolves. Bring to the boil, brush down edges of pan using a pastry brush dipped in water, and cook until dark caramel in colour (4-5 minutes), remove from heat and stir in hazelnuts. Pour onto a lightly oiled oven tray, cool completely, then coarsely chop and set aside.
Preheat oven to 180C. Using an electric mixer, beat butter and sugar until pale and fluffy, add vanilla and egg and beat until smooth. Stir in milk, hazelnut meal and baking powder and mix until smooth. Transfer mixture to a piping bag fitted with a 1cm-diameter nozzle and pipe 1.5cm-diameter rounds onto baking paper-lined oven trays. Bake until golden (12-15 minutes), cool for 2 minutes.
Meanwhile, for espresso icing, combine all ingredients in a small saucepan and stir over low heat until smooth and just warm. Add four biscuits at a time to icing and, using a fork, turn to coat, drain excess icing, then place on a wire rack over a tray, put a small piece of hazelnut praline on each and let stand until set. Store in a single layer in an airtight container. Biscotti will keep for up to 1 week.