Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line two large baking sheets with baking/greaseproof paper.

First, toast the hazelnuts: Place the hazelnuts on a lined baking sheet and spread them out into an even layer. Bake at 350ºF (180ºC) for 12-14 minutes, stirring occasionally, until they are a golden colour and their skins start loosening. Once toasted, allow to cool slightly on the baking sheet, then transfer them into a clean tea towel and rub them vigorously to remove their skins. Discard the skins, allow the hazelnuts to cool completely, and then grind them finely in a food processor or blender. Set aside until needed.

In a large bowl, using a wooden spoon, mix together the softened butter, light brown soft sugar and vanilla bean paste until combined. Don’t cream the butter – just stir it all together until you get a homogeneous mixture.

Sift together the gluten free flour blend, ground toasted hazelnuts, xanthan gum and salt, and add them to the butter-sugar mixture. Mix well with a wooden spoon until the dough starts coming together, then knead it by hand until smooth.

Roll out the cookie dough between two sheets of baking/greaseproof paper to a thickness of about 5mm.

Once you’ve rolled out the dough to a thickness of about 5mm, cut out the cookies using a 2 inch (4cm) round cookie cutter. Re-roll the scraps until you use up all the dough – you should get a total of 64 individual cookies (that will give 32 sandwich cookies).

Transfer the cookies onto the lined baking sheet(s), spacing them out slightly (leave about 1cm/½ inch of space between them).

One baking sheet at a time, bake at 350ºF (180ºC) for 12-14 minutes until light golden brown.

Allow the cookies to cool on the baking sheet for about 5 minutes, then transfer to a wire cooling rack to cool completely.

Place the chopped milk chocolate into a heat-proof bowl.

In a saucepan, bring the double/heavy cream just to the boil, then pour it over the chocolate, making sure that the cream covers the chocolate as much as possible. Allow to stand for 2-3 minutes, then stir together until smooth and glossy.

Chill the ganache in the fridge for about 15 minutes with occasional stirring until it firms up slightly and reaches a spoonable/pipeable consistency.

Transfer the ganache into a piping bag fitted with a small round nozzle and pipe dollops of ganache onto the flat (under)side of half of the cookies (about 6-7g of ganache per cookie).

Sandwich with the other half of the cookies, so that the flat (under)sides are facing each other.