In a mixing bowl, combine 1 cup of all-purpose flour, 2 tablespoons of instant coffee, 1/2 cup of powdered sugar, and 1 tablespoon of cornstarch. In a separate bowl, cream together 1/2 cup of room-temperature butter and 1 egg yolk until smooth and creamy. Gradually add the dry ingredients to the butter mixture, mixing until a soft dough forms, lustrous and slightly tacky.

Transfer the dough onto a lightly floured surface and knead gently until smooth, which should take about 2-3 minutes. Shape the dough into a log about 1-2 inches in diameter. Cut the log into approximately ½ inch cubes (about 8g each) and roll each piece into an oval shape resembling a coffee bean. Use a knife to gently indent the center of each oval to mimic the look of a coffee bean.

Arrange the shaped cookies on a parchment-lined baking sheet, ensuring they are spaced apart. Cover the baking sheet with plastic wrap and place it in the refrigerator for at least 1 hour.

Preheat your oven to 350°F (175°C). Once chilled, bake the cookies in the preheated oven for about 12 minutes.

After baking, remove the cookies from the oven and allow them to cool on the baking sheet for about 5 minutes. Then, transfer them to a wire rack to cool completely.