Make the cookie dough. Mix together flour, ground hazelnuts and salt in a bowl.
Add butter and syrup and knead briefly just until you get a soft dough that sticks together. If it's too wet or sticky, add more flour. But not too much, the dough has to stay soft.
Wrap in cling foil and leave in fridge to chill for about 15 minutes
Make small cookie dough balls, place them on lined baking sheet and flatten with bottom of a glass. If it is sticky, use some flour when rolling the balls to prevent them to stick to the glass
Bake on 160 celsius or 320F, on fan assisted mode
They are done when the edges start to brown. Leave them to cool down before assembling
Prepare the filling: place ground walnuts and vanilla in a bowl and add hot milk and syrup. Mix until you get smooth cream. It will be runny but it will become thicker as it cools down
Use approximately a teaspoon of filling for each cookies sandwich. Let the cookie sandwiches to firm up a bit when assembled. The filling will firm up and make the cookies not come appart.
Prepare the chocolate glaze: Place cocoa butter in a bowl and put it on a pan with boiling water to melt. When melted, add rest of ingredients and mix until smooth.
dip top of each cookie sandwich in chocolate and decorate with one hazelnut or walnut.