In a large mixing bowl, combine 1 cup of all-purpose flour, 2 tablespoons of instant coffee, 2 tablespoons of cornstarch, and ½ cup of powdered sugar. Make a well in the center, add the egg yolk, and softened ½ cup unsalted butter. Use a fork or your fingers to mix until the mixture resembles coarse crumbs, ensuring all ingredients are well incorporated.

Once your dough is ready, press it together until smooth. Roll the dough into a log shape, and then slice into ½ inch cubes, each weighing approximately 8 grams. Take each cube and gently roll it into an oval shape to mimic a coffee bean. Use a knife to create a midline along the length of each cookie for that classic touch.

Place the shaped coffee bean cookies on a parchment-lined baking sheet, ensuring they have enough space to spread slightly. Cover the baking sheet with plastic wrap and chill in the refrigerator for about 1 hour; this step is crucial for keeping their shape while baking.

Preheat your oven to 350°F (175°C). Once the cookies have chilled, remove them from the refrigerator. Bake the cookies in the preheated oven for approximately 12 minutes, or until they are lightly golden around the edges. Keep an eye on them to avoid over-baking.

After baking, transfer the cookies to a wire rack to cool completely. Allow them to sit for at least 15 minutes before serving, which will enhance their texture.