Melt the butter in a medium saucepan over medium heat. Stir constantly until it turns golden brown and smells nutty, about 4 to 5 minutes.
1 cup unsalted butter
Remove the pan from the heat and pour the brown butter into a heat-safe bowl. Let it cool for about 10 minutes.
In a large mixing bowl, combine the cooled brown butter and brown sugar, beating until the mixture is smooth and creamy.
1 1/2 cups light brown sugar
Add the eggs one at a time, mixing well after each addition.
2 large eggs
Stir in the vanilla extract and instant coffee until fully combined.
2 teaspoons vanilla extract, 1 teaspoon instant coffee
In a separate bowl, whisk together the flour, baking soda, and salt.
2 1/2 cups all-purpose flour, 1 teaspoon baking soda, 1/2 teaspoon salt
Slowly add the dry ingredients to the wet ingredients, mixing just until the dough comes together.
Gently fold in the chopped dark chocolate chunks until they're evenly distributed throughout the dough.
1 1/2 cups chopped chocolate
Cover the bowl and chill the dough for at least 30 minutes (but 2 hours or more is recommended)
When ready to bake, preheat the oven to 350°F and line your baking sheets with parchment paper.
Scoop out 2-tablespoon sized portions of dough and place them on the baking sheets, leaving about 2 inches between each one.
Bake the cookies for 10 to 12 minutes, until the edges are golden brown and the centers look slightly underbaked.
Let the cookies cool on the cookie sheet for 5 minutes before transferring them to a wire rack to cool completely. If you'd like, sprinkle a little flaky sea salt over the tops while they're still warm.