Add the butter and both sugars to a large mixing bowl or the bowl of your stand mixer. Cream together until well combined and slightly fluffy.
Add the eggs and egg yolks and vanilla. Beat until well mixed.
Gradually add the flour, baking soda, cornstarch, salt and espresso powder. Mix until all the dry ingredients are incorporated with no streaks of flour but don’t over mix.
Stir in the butterscotch chips.
Cover the dough and chill for 2 - 3 hours.
When you are ready to bake, preheat the oven to 350 degrees and line your baking sheets with parchment paper.
Drop the dough by tall mounds. Use about 2 tablespoons per cookie.
Bake for 9 - 11 minutes. You want the bottom edges to be very slightly brown and the middles to be soft and puffy. Don’t over bake or the cookies will be dry. Cool the cookies for a few minutes on the baking sheets and then transfer to cooling racks to cool completely. Once they have cooled sufficiently you can place them on parchment to await the chocolate bottom process.
Once all are cooled, place 2 cups semisweet chocolate chips and 1 cup butterscotch chips and 2 teaspoons of coconut oil in a microwave-safe bowl. Microwave on 50% power until melted. Stir at least every minute. Allow the chocolate to cool for a couple of minutes.
Place clean parchment paper on baking sheets or on the counter. Drop 1 - 2 teaspoons of the chocolate mixture on the parchment.
Place a cookie on a mound of melted chocolate and gently press down turning the cookie counterclockwise (or clockwise) until the chocolate has been squished and spread to the cookie’s edge.
Allow the chocolate to set up on the counter or place the cookies in the freezer for a few minutes to speed things up.
Once the chocolate has set, carefully peel the cookies from the parchment paper.