Break up the milk and plain chocolate and place it in a heat proof bowl and then gently melt it in a microwave/bain-marie. Heat the double cream in a saucepan until simmering and then pour it over the melted chocolate and mix until combined. Beat with an electric mixer to remove any chocolate lumps. Place in the fridge to set.
Place the icing caster sugar in a non-stick pan and gently heat until melted and caramelised and then pour it over the roasted hazelnuts. Once it has cooled completely, break it up and then blitz it in a liquidiser to make a praline powder.
Once the chocolate has set, mix in the praline and salt.
Preheat your oven to 190 degrees celsius.
Place the softened butter, plain flour, icing sugar and cornflour in a large bowl and combine with a wooden spoon until a very soft dough has formed.
Fit the star nozzle in the icing bag and then fill the bag with the dough. Pipe rose swirls on a non-stick baking sheet and then place on the middle shelf of your oven and bake for approximately 10mins until golden brown.
Once completely cool, sandwich two together with the chocolate praline.
