1. In a large bowl, whisk together the all-purpose flour, baking soda, cornstarch, and salt until well combined. Set aside.

2. In a separate medium bowl, whisk the melted butter, light brown sugar, and granulated sugar until no brown sugar lumps remain. Whisk in the large egg, then the extra egg yolk. Finally, whisk in the pure vanilla extract.

3. Pour the wet ingredients into the dry ingredients and mix with a large spoon or silicone spatula until just combined. Gently fold in the chocolate chips, doing your best to spread them evenly. Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 3 hours, or preferably overnight (up to 3-4 days).

4. Once dough is chilled, remove from refrigerator and let soften at room temperature for about 10 minutes. Preheat oven to 325°F (163°C). Line two large baking sheets with parchment paper or silicone baking mats.

5. Roll the chilled dough into balls, about 1.5 Tablespoons each. Make a thumbprint in one dough ball and press a Rolo candy inside. Cover the Rolo with another dough ball, molding them together until completely sealed. Gently press down on the large cookie dough ball to flatten slightly. Press a few extra chocolate chips on top if desired. Sprinkle with coarse sea salt or flaky sea salt.

6. Place 7-8 assembled cookie dough balls onto one prepared baking sheet, leaving enough space. Put the other baking sheet with remaining dough back in the refrigerator. Bake the cookies for 12-13 minutes. They will look very soft and slightly underbaked.

7. Allow to cool on the cookie sheet for 10 minutes before transferring to a wire rack to cool completely. If any cookies look too puffy, gently press down on them a little more with the back of a spoon.