Preheat oven to 350 degrees. Line two baking sheets with parchment paper (or lightly grease / spray with nonstick cooking spray).
Combine 1 tablespoon instant coffee and 1 teaspoon hot water (from the tap is fine) in a small bowl. Mix until coffee is fully dissolved. Set aside.
Use a stand mixer to cream together butter, brown sugar, and salt until light and fluffy.
Mix instant coffee / water mixture and vanilla extract into butter mixture.
Add flour to butter mixture in two batches.
Mix chopped chocolate into dough until well combined.
Roll a level tablespoon of dough into a ball, then flatten (using fingers) to about ½-inch thick. Repeat with remaining dough, placing cookies about 1-inch apart on baking sheet.
Bake cookies just until lightly browned on bottom, about 10 to 12 minutes. Let cool on baking sheet for 5 minutes, then transfer to a baking rack to cool completely before decorating.
Prepare Drizzle:
Combine 2 teaspoons instant coffee, vanilla extract, and 5 ½ teaspoons water until coffee in a medium bowl. Mix until instant coffee is dissolved.
Stir in powdered sugar, then mix until smooth.
Transfer cookies back to parchment lined baking sheets (or place backing rack over a baking sheet). Drizzle glaze over cookies using a decorating bulb, spoon, pastry bag, or zip top bag with corner snipped off.
Let glaze set, then transfer cookies to an airtight container to store. Enjoy!
Notes
When chopping the chocolate, make sure to cut it into chunks. That way, the pieces will stand out more in the cookies and give them a stronger chocolate flavor.To measure flour, lightly spoon it into a dry measuring cup, then use a knife (or something else with a straight edge) to level off the top. Do not scoop the measuring cup into the flour ... you'll end up packing the flour, and the cookies will turn out dry.As you mix the cookie ingredients, make sure to stop occasionally to scrape down the mixer's bowl and paddle with a spatula.Test drizzle on a piece of parchment paper before decorating cookies. It should hold a line when drizzled. If it's too thin, add more powdered sugar. If it's too thick, thin with an extra drop or two of water. You should have enough drizzle for about two batches of cookies.Check out the info before this recipe card for helpful tips, variations, additional cookie recipes, and more!