For whole hazelnuts, I've used skinless hazelnuts here. I toast them in the oven at 170°C for 16 to 18 minutes.
To break them up, I gently crush them with a rolling pin. I grilled a lot more than 100g, as I often use them in salads!
For the cookies, place the semi-salted butter in a saucepan.
Cook gently until it takes on a lovely nutty color, without burning the bottom of the pan.
Set aside to cool. Place the brown sugar, vanilla, semi-skimmed milk and 60g egg in a bowl.
Mix well, then pour in the hazelnut powder.
When the butter is no longer too hot, pour in 90g, which should be the weight at this point. You started with 125g, but some of it cooked off and evaporated.
Mix and pour in the flour.
Mix, then add the 100g of crushed toasted hazelnuts.
If the dough is too soft at this stage, chill it for a quarter of an hour. Then scoop out the balls, here with an ice-cream scoop, and place them on a baking sheet lined with parchment paper.
Flatten them slightly by hand.
Then bake for 10 to 12 minutes at 170°C over fan assisted heat.
The center should appear slightly undercooked. To make them rounder, I twist a small circle (or upside-down glass) around each cookie.
They will keep perfectly well at room temperature in an airtight tin for 5 days.