Preheat oven to 350°
Cut butter into tablespoons so it will melt evenly, in a microwave-safe bowl add butter and microwave about 25 seconds, you do not want to "boil" the butter, it should almost be all melted but not completely liquidy. Mix it with a spoon as the hotter spots will slowly melt the other areas of butter not yet completely melted.
Stir in the instant coffee granules until they completely dissolve.
In the large bowl of a mixer add butter, granulated sugar, and brown sugar and mix until combined well.
Beat in the vanilla and egg.
Add in the flour, cornstarch, baking powder, and salt and mix on low at first then once it's added in mix on medium to fully combine.
Stir in chocolate chunks.
On parchment-lined baking sheet add cookie dough in 2 tablespoon portions spread out 2 inches apart for even baking.
Bake cookies for 12-14 minutes (12 will give you chewier cookies, 14 will be firmer cookies)
Allow cookies to cool on baking sheets then serve.