01 - Preheat oven to 350°F. Line a baking sheet with parchment paper and set aside.
02 - In a medium bowl, whisk together the almond flour, coconut flour, powdered erythritol, baking powder, and fine sea salt until evenly distributed.
03 - In a large bowl, combine the hazelnut butter, melted butter, egg, and vanilla extract. Beat until the mixture is smooth and well incorporated.
04 - Gradually add the dry ingredient mixture to the wet ingredients, stirring with a spatula until a soft, cohesive dough forms.
05 - Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them about 2 inches apart. Gently flatten each portion with your palm or the back of a spoon.
06 - Bake for 10 to 12 minutes, or until the edges are lightly golden. Let the cookies cool on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely.
07 - In a small bowl, whisk together the hazelnut butter, powdered erythritol, almond milk, and vanilla extract until smooth and pourable. Add additional almond milk, one teaspoon at a time, if a thinner consistency is needed.
08 - Drizzle the mixture over the fully cooled cookies. Allow the drizzle to set for 10 minutes before serving.