Hazelnut Chocolate Chip Cookies

Toast the hazelnuts in a small pan on low to medium heat until they turn golden, stirring often, 5-10 minutes. Set aside and cool. Place the hazelnuts in a sturdy Ziploc bag, seal them, and break them into small pieces with a mallet.
Preheat the oven to 350F. Line 2 cookie sheets with parchment paper.
Whisk together the flour, cornstarch, baking soda, and salt in a small bowl. Set aside.
Place the cubed butter and the sugars in a large bowl and mix with an electric mixer until everything creams together, 3-5 minutes. Add the egg, egg yolk, and vanilla extract and mix to combine, about 30 seconds.
Add the dry ingredients to the wet, in thirds, using the mixer to combine. The batter will become increasingly thick. Stir in the hazelnuts and half the chocolate chips when you add in the remaining dry ingredients. Combine again; pour in the remaining chocolate chips, and finish combining all ingredients with the mixer.
Use a 2" diameter cookie scoop to place 8-10 cookies onto each cookie sheet. Flatten each one slightly with the palm of your hand. Place the sheets on the oven's middle rack and bake for 10-14 minutes until they turn lightly golden around the edges and on top.
Remove the cookie sheets from the oven and allow them to cool for a couple of minutes before transferring them to a wire rack to cool completely.