Preheat your oven to 350°F (175°C). Line your baking sheet with parchment paper or a silicone baking mat.
In a large mixing bowl, use a hand or stand mixer to cream together ½ cup of unsalted butter and 1 cup of white granulated sugar until light and fluffy, about 2-3 minutes.
Add 1 egg, 1 egg yolk, and 1 teaspoon of vanilla extract to the creamed mixture. Mix until fully incorporated.
In a separate bowl, whisk together 2 cups all-purpose flour, ⅓ cup unsweetened cocoa powder, ½ teaspoon baking soda, and ¼ teaspoon salt.
Gradually add the dry ingredients to the wet mixture, mixing just until combined.
Pour 2 tablespoons white granulated sugar into a small bowl. Form dough into 1-inch balls and roll each in sugar until coated.
Place dough balls on the baking sheet about 2 inches apart. Bake for 8-10 minutes until edges are set but centers soft. Remove from oven and immediately press a Hershey’s Kiss into the center of each cookie.
Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
