Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, cream the softened butter, granulated sugar, and brown sugar together until light and fluffy, about 3 minutes.
Beat in the egg yolk and vanilla extract until fully incorporated.
In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually add the dry ingredients to the butter mixture, mixing on low speed until a soft dough forms.
Roll the dough into 1-inch balls and place them on the prepared baking sheet, spacing them about 2 inches apart.
Use your thumb or the back of a rounded teaspoon to press a deep indentation into the center of each dough ball.
Bake for 10 to 12 minutes, or until the edges are set. If the centers have puffed up during baking, gently press them down again with the back of a spoon immediately after taking them out of the oven.
While the cookies cool, place the unwrapped caramels and heavy cream in a small saucepan over low heat. Stir constantly until the mixture is smooth and melted.
Spoon approximately 1/2 teaspoon of the warm caramel into the center of each cookie.
Once the caramel has set, melt the semi-sweet chocolate chips and drizzle the streaks over the top of the cookies using a piping bag.