Add the butter to a pot and heat it over medium heat. Allow the butter to melt and come to a simmer. Simmer until the butter is giving off a nutty scent and has browned. The whole process should take about 5 minutes. Measure out 6 tablespoons of melted brown butter and place in a small bowl. (The extra two tablespoons of butter should cook off during the browning process, but it is possible to have a little bit left over after you've measured out the 6 tablespoons.)
½ cup (112 g) unsalted butter
Refridgerate until the butter has reached the same consistency as regular softened butter.
Preheat the oven to 350 degrees.
In a medium bowl, whisk together the flour, baking powder, baking soda and salt. Then set aside the flour mixture.
¾ cup + 2 tablespoon (109 g) all-purpose flour, spooned and leveled, ¼ teaspoon baking powder, ¼ teaspoon baking soda, ¼ teaspoon salt
In a large bowl, cream the cooled brown butter, brown sugar and granulated white sugar together with an electric mixer on high speed until light and fluffy, 2-3 minutes. (You can also use a stand mixer fit with a paddle attachment.)
6 tablespoon (83 g) light brown sugar, 2 tablespoon (25 g) granulated white sugar
Add in the egg yolk and vanilla and mix on medium high speed until pale in color and fluffy, 1-2 minutes.
1 egg yolk, at room temperature, ½ tablespoon vanilla
Add the dry ingredients to the wet ingredients and mix on low speed just until combined.
Mix the chocolate chips into the dough with a rubber spatula.
⅓ cup (70 g) semi-sweet chocolate chips
Form the dough into a large ball then press it down slightly so it resembles a disk about 1 ½ inches thick.
Transfer the dough to the center of a cookie sheet lined with parchment paper. Sprinkle extra chocolate chips on top and bake the cookie for 21-24 minutes until golden brown.
2 tablespoon (25 g) semi-sweet chocolate chips for sprinkling on top of cookie before and after baking
After baking, add a few more chocolate chips on top along with flaky sea salt. Let the cookie cool on the baking sheet for 15 minutes, then transfer to a cooling rack to completely cool, or just dig in straight from the cookie sheet.