Let the butter come to room temperature. Take the butter out of the refrigerator about 30–60 minutes ahead of time: soft but not melted is ideal.

Finely grind the hazelnuts. Use a food processor to make fine crumbs; if you don’t have one, chop the nuts with a sharp knife or crush them in a mortar and pestle. You don’t want nut butter, just small pieces.

Beat the butter mixture. Put the soft butter, sugar, and salt in a bowl and mix with a whisk or mixer until creamy.

Add the milk. Pour the milk in all at once or in two additions and stir briefly until the mixture is smooth.

Sift in the flour and make the dough. Sift the flour over the bowl, add the finely ground hazelnuts, and knead with your hands or a spatula until a cohesive dough forms. Do not knead longer than necessary — it should just come together.

Wrap and let rest. Shape the dough into a flat disk, wrap in plastic wrap, and let rest in the refrigerator for 45 minutes. (Flattening it makes it easier to roll out later.)

Preheat the oven to 338 °F. Turn the oven on just before the resting time is almost over so it will be at temperature when you start baking.

Briefly knead and roll out. Knead the chilled dough very briefly on a floured work surface and roll out to about 3/16 inch thick (or to your preference).

Cut out the cookies. Use a round cutter and place the rounds on a baking sheet lined with parchment paper. Leave some space between the cookies and repeat with the remaining dough.

Bake the cookies. Bake for 12–15 minutes in the preheated oven until lightly browned and cooked through. Remove the baking sheet from the oven and let the cookies cool on a wire rack for 30 minutes.