Place butter in a light-colored saucepan over medium heat. Cook, stirring constantly, until the milk solids turn golden brown and the butter develops a nutty aroma. Transfer to a heat-proof bowl and chill until it reaches a soft, spreadable consistency.

Place toasted hazelnuts in a food processor. Pulse 50g into a fine meal. Coarsely chop the remaining 75g by hand to maintain texture.

In a stand mixer fitted with the paddle attachment, cream the browned butter, brown sugar, and white sugar on medium-high speed for 4 minutes until aerated.

Add the egg and vanilla extract to the butter mixture. Beat for 1 minute until the emulsion is light and pale.

Whisk together the flour, hazelnut meal, baking soda, and salt in a separate bowl.

Reduce mixer speed to low and gradually add the dry ingredients. Mix until just combined, then fold in the chopped hazelnuts by hand.

Scale the dough into 30g portions and roll into spheres. Place on a tray and refrigerate for 30 minutes to prevent excessive spreading during baking.

Preheat a convection oven to 350°F (175°C). Line two baking sheets with professional-grade parchment paper.

Space dough balls 2 inches apart on the sheets. Bake for 11-13 minutes until the edges are firm and deeply golden brown.

Transfer cookies to a wire rack to cool completely. This step is critical for developing the 'crunch' factor.

For the ganache: Heat heavy cream in a small saucepan until it reaches 185°F (85°C). Pour immediately over the chopped chocolate in a glass bowl.

Let the chocolate and cream sit undisturbed for 3 minutes. Whisk gently from the center outward until a glossy, stable emulsion is formed.

Dip each cooled cookie halfway into the ganache at a 45-degree angle. Allow excess to drip off before placing on clean parchment.

Let the ganache set at room temperature for 30 minutes or refrigerate for 10 minutes before serving.