In a medium mixing bowl, sift the flour, cocoa powder, baking soda, baking powder, and salt. Gently whisk and set aside.
In a large mixing bowl, add the granulated sugar, brown sugar, butter and vanilla and beat with a hand mixer for 2-3 minutes. The sugars and butter should resemble cream.
Next, add the egg and yolk, and beat until well combined.
Then, add your "sifted flour mixture" into your wet batter and mix with a wooden spoon or rubber spatula until combined. Be sure not to over mix. Next, fold in your chocolate and nuts.
Transfer the cookie dough to a fridge and let chill for at least 30 minutes to allow the flour to hydrate (Pro tip: Allowing your dough to refrigerate for 2-4 hours (or overnight) will result in the best flavored cookie; however, 30 minutes works just fine.)
Remove your chilled dough and preheat your oven to 350°F. Line a nonstick baking sheet with parchment paper. Then, scoop the dough into the lined baking sheet with a large (3 tablespoon sized) cookie scooper. The dough should be about 3 inches apart.
Bake the cookies in the preheated oven for 13-16 minutes or until the edges of the cookies are set and the center is slightly puffed. Top with flaky sea salt as soon as you take them out of the oven to cool. Let rest for about 10-15 minutes or until set.
Once cooled, enjoy and feel free to add a comment on my blog! Also, be sure to share your photo on instagram and tag @butterloveandsalt! We would love to see how your cookies come out!