Preheat your oven to 375°F.
Add the all-purpose flour, Dutch process cocoa powder, salt, and baking powder to a medium mixing bowl. Pour the ½ tsp of instant coffee into the palm of your hand. Pinch the coffee between your fingers to break it down even further as you add it to the bowl. Whisk together all dry ingredients and set aside.
1 cup all-purpose flour, ⅓ cup Ghirardelli Unsweetened Dutch Process Cocoa Powder, ½ tsp salt, 1½ tsp baking powder, ½ tsp instant coffee
Add the softened salted butter, white granulated sugar, and light brown sugar to a large mixing bowl. Cream together using a hand mixer on low/medium speed (approx. 2-3 minutes).
½ cup salted butter, ⅓ cup white granulated sugar, ½ cup light brown sugar
Add the egg, egg yolk, vanilla extract, and milk. Mix on medium speed until well combined, making sure that you're scraping down the bowl using a spatula or spoon periodically.
1 egg, 1 egg yolk, 1½ tsp vanilla extract, 1 tbsp milk
Add the dry ingredients to the wet ingredients and mix on the lowest speed until just combined. Scrape down your bowl with a spatula or spoon, paying particular attention to any dry ingredients stuck to the bottom. Add the chocolate chips and mix on low until they are just incorporated into your dough. Do not overmix.
1 cup semi-sweet chocolate chips
Place a silicone baking mat or parchment paper on your half sheet pan. Scoop the dough onto the pan using a #40 cookie scoop (about 1.5 tbsp of dough). This dough is quite sticky, so I highly recommend using a scoop. I typically bake 6-8 (max!) cookies per sheet pan. Do not press the cookies down as they will spread on their own. (See Note 2 below.) Bake the cookies for 10 minutes at 375°F, or until the edges look set while the center is still soft. The centers of the cookies should no longer look shiny when the cookies are done. Allow the cookies to cool on the sheet pan for 5 minutes once you remove them from the oven.
Optional- If you'd like to add some extra chocolate to this recipe and make your cookies look particularly aesthetically pleasing, lightly press 5-6 chocolate chips into the top of the cookies while they are still hot from the oven.
After the cookies have cooled slightly on the sheet pan, transfer them to a wire cooling rack to finish cooling. Then enjoy! Store these cookies in an airtight bag or container once completely cooled.