Line a baking sheet with parchment paper. Set aside.
Heat the butter in a small saucepan set over medium-low heat. When the butter has melted completely, whisk frequently and continue to heat until the butter begins to foam and brown bits begin to form. Keep a close eye on the butter and remove from heat as soon as it turns a golden amber color, after about 10 minutes. Pour into a heat-safe container and place in the refrigerator to cool for 10-15 minutes.
1 cup unsalted butter
In a large mixing bowl, whisk together the all-purpose flour, baking soda, and sea salt. Set aside.
2⅓ cups all-purpose flour, 1 teaspoon baking soda, ¼ teaspoon fine sea salt
When the butter is cool to the touch, add it to a separate mixing bowl and use a hand-held mixer (or a stand mixer with a paddle attachment) to mix the cooled butter, brown sugar, and granulated sugar.
1 cup brown sugar, ⅔ cup granulated sugar
Add in the eggs and vanilla extract. Mix well.
2 large eggs, 1½ teaspoons pure vanilla extract
Add the butter mixture to the flour mixture and mix until just combined. Fold in the white chocolate chips and semisweet chocolate chips.
1 cup semisweet chocolate chips, ½ cup white chocolate chips
Use a cookie scoop to scoop the dough and place it on the prepared baking sheet. Chill in the refrigerator for 30 minutes.
While the cookies chill, preheat oven to 350°F. Place the cookies 1 inch apart on a baking sheet and bake the cookies for 10-12 minutes, or until the edges are set and beginning to brown.
Remove the cookies from the oven and immediately sprinkle with flake sea salt if desired. Allow to cool on the baking sheet for 5 minutes before removing to a wire rack to cool completely.
Flake sea salt