Preheat your oven to 350°F. Spread hazelnuts on a baking sheet and toast for 6–8 minutes until fragrant.

Let hazelnuts cool completely. In a food processor, pulse the hazelnuts with granulated sugar and salt until finely ground.

Add whole wheat pastry flour, all-purpose flour, and cornstarch to the processor and pulse until combined.

Add vanilla extract, lemon zest, and softened butter, pulse until a soft dough forms.

Transfer the dough into a gallon freezer bag, flatten into a slab, seal, and refrigerate overnight.

Roll out the chilled dough to about 1/4-inch thickness and cut into 1-inch rounds.

Whisk the egg and water for an egg wash, brush each cookie lightly, and sprinkle with turbinado sugar.

Reduce the oven to 325°F and bake for 10–12 minutes until edges are light golden. Cool on the baking sheet for 5 minutes.

Chop the dark chocolate and place it in a bowl. Heat heavy cream until simmering, pour it over chocolate, add bourbon and salt, and whisk until smooth.

Chill the ganache for 10–15 minutes until thick, then pipe a dollop onto each cookie and let set.