In a mixer bowl with paddle attachment, place butter and salt. Mix on medium speed until creamy.
Add sugar and continue to mix until well blended. Add flour, cornstarch, and vanilla extract. Mix until just combined and mixture comes together to form clumps.
On a floured surface, drop dough on top and mold into a cylinder shape.
Wrap dough with plastic wrap and place in fridge for 30 minutes, until the dough is chilled and firm enough to cut.
Once ready, remove plastic and place on cutting board. Using a knife, cut 1/4 inch circular slices.
Transfer cut cookies on to a baking sheet with parchment paper or silicone paper on top. Place cookies 1/2-1 inch apart from one another. Bake at 350 degrees F at the middle rack for 15-20 minutes or until the bottom and edges are browned.
Remove from the oven and allow the cookies to cool to room temperature. You may store in an air-tight container if you're making this recipe over two days.
In a double boiler set up*, melt chocolate chips until smooth and creamy.
Using a muffin pan, line with cupcake liners. Drop 1 tbsp of melted chocolate at the bottom of each liner. Top with one shortbread cookie.
Unwrap each caramel candy and using thumbs, flatten to fit on top of the shortbread cookie. Place on top. Add another tablespoon of melted chocolate on top of each candy. Top with sea salt sprinkling if desired.
Place in refrigerator for 1 hour or until chocolate covering is hardened.
Notes
For double boiler, I use a small pot with a fitted bowl on top. I fill the pot with water and set to low boil, making sure the water does not flow into the top section and spoil the chocolate.