Caramel Sauce: Mix heavy cream and vanilla together. Set aside.

Caramel Sauce: Add sugar and water to a small saucepan and give it a small mix together. Put on medium heat. After the mixture is on the heat, DO NOT mix it anymore.

Caramel Sauce: Heat until sugar is totally dissolved, and mixture has turned a deep amber color.

Caramel Sauce: Remove from the heat and pour in heavy cream mixture while quickly whisking it all together. There will be a lot of steam at this point and the sugar will be VERY hot. Use a large whisk so your hand is not too close, and DO NOT touch or taste the caramel.

Caramel Sauce: Add in salt, and transfer to a small jar to let cool completely. This will take hours.

To make the cookies, whisk flour, baking soda, corn starch, and salt together in a large bowl, then set aside.

Mix sugars together with the melted butter until completely smooth and lump free. Add in egg, egg yolk, and vanilla. Mix again until smooth.

Add 1 tbsp espresso powder to 1 tbsp water. Whisk together, then add to butter mixture. Whisk until completely incorporated.

Add dry ingredient mixture to butter mixture. Slowly fold in until only a little bit of flour is still visible. Add in chocolate chips, then finish folding together.

Add caramel sauce, and gently swirl into cookie dough. There should be visible streaks of caramel throughout the dough.

Chill for at least 3 hours (preferably overnight).

Once dough is chilled, preheat oven to 350. Roll dough into balls of about 3-4 tbsp each. Roll into balls that are taller rather than wider.

Bake for about 10-12 minutes. The cookies will look underdone when you take them out, and they will stay soft.