Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal. Lightly spray the parchment with non-stick cooking spray.

In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.

In a large bowl, using an electric mixer, cream together the softened butter, granulated sugar, and brown sugar on medium speed until light and fluffy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract and the dissolved espresso powder (2 tbsp espresso powder mixed with 1 tbsp hot water). Mix until just combined.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix. If using, fold in the mini chocolate chips.

Press the cookie dough evenly into the prepared baking pan. You can use the back of a spoon or your hands (lightly floured if sticky).

Bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs, but not wet batter. Do not overbake to ensure soft, chewy bars.

Remove the pan from the oven and let the bars cool completely in the pan on a wire rack before attempting to glaze.

Once the bars are completely cool, prepare the glaze. In a small bowl, whisk together the sifted powdered sugar, the dissolved espresso powder (1 tbsp espresso powder mixed with 1 tbsp hot milk or water), and vanilla extract.

Gradually add milk or cream, 1 tablespoon at a time, whisking until you reach a smooth, pourable consistency. You may not need all 3 tablespoons.

Pour the glaze over the cooled cookie bars and spread evenly with a spatula or knife. Let the glaze set for at least 30 minutes before slicing and serving. For faster setting, you can place them in the refrigerator.