Combine butter, sugar, egg yolk, and vanilla into a medium sized mixing bowl and beat on medium speed for a few minutes, scraping the sides of the bowl occasionally. This mixture needs to be nice and creamy before you add the flour.
Slowly add the flour to this mixture, mixing on low as you add it. Only combine about 1/4 cup at a time.
Cover mixing bowl with plastic wrap and refrigerate dough for at least one hour.
For the caramel filling
Unwrap caramel candies and place into a microwave-safe bowl. Heat in microwave for 45 seconds, until soft.
Pour in whipping cream and mix together until completely combined.
Spoon 1/2 tbsp. into the well of each cookie. Let cool and set.
For milk chocolate topping
Melt chocolate chips in a microwave-safe bowl. Remove from microwave and stir until creamy.
Spoon melted chocolate into the bottom corner of a ziplock plastic bag. Snip a small piece of the corner off with scissors, and push chocolate towards snipped corner.
Gently squeeze bag until chocolate comes out of the corner, and carefully drizzle over each cookie.
Let chocolate cool and set completely.
Notes
If you aren't so much into the presentation of these cookies, you are welcome to dip each one caramel-side-down into the chocolate to coat the tops of them. The flavor is all there and it's less work!Adapted from Twix Thumbprint Cookies