Preheat oven to 375℉.

Cream together the butter and sugar on medium-high speed until light in color and fluffy. Beat in egg yolks and vanilla extract until fully incorporated. Mix in flour and salt until the dough comes together.

Put the trays in the fridge for about 30 minutes to firm up. (Do not skip this step because if your dough is too warm it will just melt into blobs that you can not fill.)

Bake the cookies for about 8-10 minutes, just until they are browning on the bottom slightly.

Once baked, put cookie trays aside and let them cool slightly before filling them.

Combine the cream, sugar, brown sugar, and corn syrup in a medium heavy duty saucepan. Mix over medium heat, stirring constantly as the sugar dissolves.

Once the mixture comes to a boil, attach a candy thermometer to the pan. Cook and carefully stir every couple minutes until the temperature reaches 245℉.

Once the temperature reaches 245℉, remove from heat, stir in salt, vanilla paste and butter until well combined and butter is completely melted.

Once all mixed in, pour the caramel into the thumbprints of the cookies. Let cool for about 20 minutes.

While caramel cools, melt the chocolate chips either in the microwave or a double boiler. Transfer to a piping bag and cut of a tiny part of the tip.

Pipe lines across cookies and then sprinkle with the sea salt.

Let chocolate set at room temperature.