To make the cookie dough

• Preheat the oven to 350 degrees.
• Cube the butter into 1 cm pieces.
• Use a hand mixer or a stand mixer fitted with the paddle attachment to cream the butter and sugar. Cream on high for 1-2 minutes, or until the mixture is smooth.
• Add in the egg and vanilla extract. Mix until combined.
• In a separate bowl, whisk together dry ingredients (flour, corn starch, salt, baking powder, baking soda).
• Add the dry ingredients to the wet ingredients in 2-3 portions. Mix until well combined, then scrape down the bowl once complete.
• Mix together the semi-sweet chocolate chips and the milk chocolate chips in a separate bowl.
• Add 1 cup of the chocolate chip mixture to the dough. Mix until combined.
• Line a cookie sheet with parchment paper, set aside.
• Roll the dough into 2-2½ inch dough balls. Gently press additional chocolate chips throughout the balled dough (avoid placing additional chocolate chips on the bottom of the cookie).
• Place the dough on the lined cookie sheet, leaving 1-2 inches between each cookie.
• Bake for 12-15 minutes or until the edges just begin to brown.
• Add more chocolate chips to the cookies immediately after taking them out of the oven, filling in any empty spaces that appeared when the cookies baked.
• Sprinkle with coarse sea salt and allow them to cool on the cookie sheet or on a cooling rack.