Step 1: Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper or silicone mats.
Step 2: In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until the mixture is smooth and pale.
Step 3: Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract and the espresso powder until fully incorporated and the powder is dissolved.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Step 6: Fold in the chocolate chips using a spatula. For the best results, chill the dough in the refrigerator for at least 30 minutes.
Step 7: Scoop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Step 8: Bake for 9 to 11 minutes, or until the edges are lightly browned but the centers still look slightly soft.
Step 9: Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. Sprinkle with flaky sea salt if desired.