Make the browned butter (see note below) or re-melt if already made. Mix in instant espresso and set aside for about 20 minutes to infuse and cool.
In a medium bowl, sift flour, baking soda, and salt.
In a large bowl, mix browned butter, brown sugar, light brown sugar, and white sugar until well blended.
Add 1 egg, beat for 1-2 minutes. Add egg yolk and vanilla extract, beat for another 1-2 minutes.
Add dry ingredients to the butter-sugar-egg mixture and mix until just combined. Be careful not to overmix.
Gently stir in chocolate chunks and chocolate chips.
Scoop out about 1/3 cup of dough, roll into balls, and place on a baking sheet. Refrigerate if time allows.
Preheat oven to 350 degrees.
Remove dough from the fridge and place on a baking sheet.
Bake for 14-16 minutes until edges are golden brown. Avoid overbaking.
Transfer cookies to a wire rack to cool. Sprinkle with Maldon salt or your favorite flaky sea salt!