With an electric mixer, beat the softened butter, brown sugar, 1/4 cup of granulated sugar, egg, syrup, vanilla and 3 teaspoons of espresso powder, for 2 minutes, until well combined.
Separately, whisk together the flour, corn starch, baking soda and salt. Add the dry ingredients to the wet, and stir everything together with a spatula into a thick dough.
Use a small cookie scoop with a release lever to scoop 24 balls of dough.
In a small bowl, combine the remaining 1/4 cup granulated sugar with 1 teaspoon espresso powder. Roll the dough balls smooth between your hands, coat them in the espresso sugar, and then flatten the balls into disks.
Cover the flattened cookie dough balls with plastic wrap, and refrigerate for 2 hours.
Preheat the oven to 350 F, position a rack in the center of the oven, and line a baking sheet with parchment paper.
Space the chilled cookies several inches apart on the baking sheet, and bake for 8 minutes. Cool several minutes on the baking sheet, then transfer to a cooling rack to cool completely. The cookies will initially look puffed when you take them out of the oven, but will settle and flatten a bit as they cool.