Prepare the dry ingredients: In a medium bowl, mix together the flour, espresso powder, cornstarch, baking soda, and salt until well combined. Set aside.

Cream the butter and sugars: In separate bowl mix, either with a stand mixer or a hand mixer, beat the softened butter and sugars on medium-high speed until the mixture becomes light, fluffy, and pale yellow, which should take about 2 minutes. Remember to scrape down the sides of the bowl occasionally.

Combine the wet and dry ingredients: Add the egg and vanilla to the creamed mixture, and beat on medium speed until they are well combined, about 30 seconds. Gradually add the dry ingredient mixture and beat on medium-low speed until just combined. Use a spatula or wooden spoon to fold in the chocolate chips until evenly distributed.

Chill the dough: Transfer the dough to an airtight container and refrigerate it overnight.

Preheat the oven and prepare the baking sheet: Preheat the oven to 350°F. Prepare parchment paper lined baking sheet.

Bake the cookies: Once the cookie dough is thoroughly chilled, remove it from the refrigerator. Scoop out and roll dough balls that are 1-inch in diameter and place them on the prepared baking sheet. Bake for approximately 10-12 minutes, or until the edges are slightly crispy and the tops are lightly golden. The centers may still appear slightly undercooked. Allow the cookies to cool on the baking sheet for about 5 minutes before serving. Optionally, but if so the best part, sprinkle a pinch of flaky salt on top before serving.