Line baking sheets with parchment paper.
In a small bowl, whisk together the flour, baking soda, and salt in a bowl and set aside.
In large bowl, beat the butter and sugars on medium speed until well combined, about 2 minutes. Add egg, yolk, vanilla extract, and vanilla paste and mix until incorporated,
Add the dry ingredients and mix on low speed until just combined. I like to stop the mixer before the flour is fully incorporated and mix the rest by hand with a spatula. Fold in the chocolate chips and walnuts.
Scoop dough onto baking sheets about 2 inches apart. I used a medium cookie scoop that is approx. 3 tablespoons, but feel free to use a smaller 2 tbsp scoop. Sprinkle with flaked sea salt. Chill the pans in the refrigerator for about 30 minutes.
While the dough is chilling, preheat the oven to 350°.
Bake for 10-13 minutes, until lightly golden on the edges. Let the cookies set for 5 minutes before transferring to a cooling rack.