Heat the oven to 180C (160C fan)/350F/gas 4.

Spread out the hazelnuts on an oven tray, then roast for 12-15 minutes, until deeply toasted. Remove, then leave to cool completely for 30 minutes or up to an hour.

Put the toasted hazelnuts, plain flour and cornflour in a food processor, then pulse a few times until the mix resembles sand – do not overprocess, otherwise you’ll end up with a paste.

Add the caster sugar, salt, vanilla paste and butter, then pulse again until the mix comes together into a dough, scraping down the sides of the bowl with a spatula as required.

Tip out the dough on to a sheet of greaseproof paper, and heat the oven again to 180C (160C fan)/350F/gas 4.

Pinch off 10g pieces of the dough and roll these into balls; if the dough is too soft to handle, cover with greaseproof paper and chill for 15-20 minutes to firm up.

Put the dough balls on two baking trays lined with greaseproof paper, leaving at least 3cm between each cookie to allow for spreading, then bake for 18-20 minutes, until lightly golden. Remove and leave to cool completely.

Meanwhile, put all the ingredients for the filling and a tablespoon and a half of lukewarm water in the bowl of a stand mixer fitted with the paddle attachment.

Start on a low speed just to combine everything, then turn up the speed to high and whisk for about five minutes, until light and creamy. (Alternatively, use a hand whisk or a wooden spoon and some elbow grease to work the filling to a creamy and pipeable consistency.)

Scrape the filling into a piping bag, then pipe (or spread with a spatula) a generous amount (about 10g, or one and a half teaspoon’s worth) on to the flat sides of half the cookies.

Sandwich with the remaining cookies flat side down, pressing down gently to squish the filling right to the edges.

Arrange on a platter and serve or, if gifting, store in an airtight tin or bag tied with a ribbon.