Preheat oven to 350 degrees F. Line two baking sheets with parchment paper.
Into the bowl of a stand mixer (or using an electric hand mixer), add cold butter, sugar, and brown sugar. Using the paddle attachment, mix on medium-high speed until well-combined and lighter in color, about 3-4 minutes, stopping once to scrape down the sides of the bowl.
Add the eggs, one at a time, and beat for an additional 2 minutes until well incorporated. Pour in vanilla extract and mix for an additional minute.
Add flour, baking soda, salt, and instant espresso powder. Mix on low speed until flour is almost absorbed.
Remove bowl from stand mixer and use a rubber spatula to mix in chocolate chips by hand. Cover and chill in the refrigerator for at least 3 hours or overnight.
Use a medium cookie scoop to place balls of dough onto lined baking sheets. Sprinkle with flaky sea salt (if using).
Bake for 10 minutes, or until cookies are just barely set in the middle.
Let cookies rest on baking sheet for 10 minutes before transferring them to a cooling rack. Store in an airtight container at room temperature for up to 5 days.