Using a flat beater mix together the softened butter and soft brown sugar. Add the salt, eggs, ground roasted hazelnuts, and flour. Place in the fridge for about 1 hr. Roll out the dough to a thickness of 3 mm then cut out using a 7 cm round pastry cutter and cook in a fan oven at 160°C (320°F) for about 15 min.
Using a flat beater work the chestnut paste and then add in one after the other the chestnut cream, chestnut purée, softened butter, and finally the inverted sugar. Mix but without causing it to swell. Using a piping bag with a bird’s nest nozzle, pipe about 30 g of chestnut mousse into 12 domed ‘flexipan’ moulds and place in the freezer for 1 hr.
Whip all the ingredients together in a beater.
Using a piping bag with a no. 9 plain nozzle pipe a bit of Chantilly onto the chestnut mousse, take a little scoop of cooked French meringue and finish the dome with the rest of the Chantilly and finally gently place the cooked hazelnut short pastry on top. Place in the deep freeze. Take the little cakes out of their moulds and decorate with a scoop of Chantilly and chocolate shavings.