Preheat Oven: Preheat your oven to 350°F and line two baking sheets with parchment paper.
Cream Butter and Sugar: In a large mixing bowl, use a hand mixer or stand mixer to beat the softened butter and ½ cup granulated sugar until light and fluffy, about 2-3 minutes.
Add Wet Ingredients: Add the egg yolk, whole egg, and vanilla extract to the butter mixture. Beat until fully combined.
Combine Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, almond flour, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Shape and Roll: Scoop about 1 tablespoon of dough and roll it into a ball. If desired, roll the ball in the additional ½ cup sugar for a crisp, sweet coating. Place the balls 2 inches apart on the prepared baking sheets.
Create Indentations: Use your thumb or the back of a small spoon to gently press an indentation into the center of each cookie.
Bake: Bake the cookies in the preheated oven for 10-11 minutes, or until the edges are lightly golden.
Cool: Allow the cookies to cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.
Fill with spread: Spoon about ½ teaspoon of chocolate hazelnut spread (as much or as little as you'd like). Sprinkle with toasted hazelnuts.
