Preheat your oven to 350 degrees F and roast the hazelnuts on a lined baking sheet for 8-10 minutes. Let them cool off for 10 minutes.

Rub off the hazelnut skins with a dish towel. Set aside 1/3 cup of the roasted hazelnuts for toppings.

Blend the remaining hazelnuts in a food processor until they reach a fine sand texture to achieve hazelnut flour. Pack 3/4 cup tightly.

Brown the unsalted butter in a small saucepan over medium heat for 7-10 minutes until brown specs form. Add the hazelnut flour, stirring for 30-45 seconds to toast.

Transfer the brown butter mixture to a large bowl, adding 1 tbsp of ice cold water. Set aside until completely cooled.

Prepare the toppings by splitting the 1/3 cup of toasted hazelnuts in halves and chopping the remaining into small chunks.

Split the Lindt chocolate bar in half. Chop one half into large chunks for topping and the other half into small chunks for the dough.

Once the brown butter has cooled, whisk in the dark brown sugar and white sugar. Then add the vanilla extract and egg.

In a medium bowl, mix the dry ingredients: all-purpose flour, salt, cinnamon, and espresso powder.

Combine the dry ingredients with the wet mixture, stirring until just combined. Add the small chocolate chunks to the cookie dough.

Chill the cookie dough in the fridge for 30-45 minutes until firm. Use a large cookie dough scoop to scoop out the dough onto a lined baking sheet, making 10 cookies.

Add toppings: place large chocolate chunks and 3 hazelnut halves on each cookie, along with chopped hazelnut chunks.

Transfer the cookie tray to the fridge for overnight to 24 hours to hydrate the dough.

The next day, preheat the oven to 375 degrees F. Bake 6 cookies at a time on a lined parchment baking tray for 12-14 minutes.

Sprinkle baked cookies with flaky sea salt before serving.