Pre-heat oven to 350F (180C). Line two cookie sheets with parchment paper.
Roast the whole hazelnuts (⅓ cup + 1 tablespoon and the 20 whole hazelnuts) for about 5-6 minutes. Move them to a clean bowl, remove 20 hazelnuts and set aside. The remaining hazelnuts place in a food processor and pulse until finely chopped (see photo). Set aside.
In the bowl of the mixer cream the butter and sugar until fluffy about 2-3 minutes.
Add the flour, chopped nuts, egg yolk, milk and vanilla. Mix just until combined into a dough.
Either place the dough in a pastry bag with a large star tip or drop by heaping teaspoonfuls (or half and half) on the prepared cookie sheets. Place a roasted whole hazelnut on each cookie round and bake for approximately 15-20 minutes or until golden. Let cool 10-15 minutes on the cookie sheet then move to a wire rack to cool completely. Enjoy!
Notes
How to store the cookies
The cookies should be stored in an airtight container and can be stored at room temperature for three or four days. They can also be stored in the fridge for up to one week.
Can you freeze them?
The cookies can be frozen in a freezer safe bag or container. They will keep for up to two months if stored properly.