Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, cream together softened butter and granulated sugar until light and fluffy, about 2-3 minutes.

Add egg yolks and vanilla extract; mix until smooth.

Gradually incorporate all-purpose flour until a crumbly dough forms, then set aside half of the dough.

Mix cocoa powder into the reserved dough until fully combined.

Roll pieces of each dough into 12-inch logs and twist them together to create a marbled look.

Shape twisted logs into a 20-inch spiraled log and cut into 1-inch sections.

Roll each cookie ball in sanding sugar and place on the prepared baking sheet, spaced about two inches apart.

Bake for 12 minutes, then gently press an unwrapped Hershey’s chocolate into the center of each cookie while warm.

Allow cookies to cool on the baking sheet for 3-5 minutes before transferring to a wire rack to cool completely.