Preheat your oven to 350°F (177°C) and line a baking sheet with parchment paper, or prep with baking spray.
In a large bowl, cream the butter, granulated sugar, and brown sugar together until light and fluffy using an electric mixer or a whisk for about 4 - 6 minutes. Make sure your melted butter is NOT hot or it will melt your chocolate!
Add in the eggs, one at a time, and mix until fully incorporated. Stir in the vanilla extract and milk.
In a separate bowl, whisk together the flour, baking soda, cornstarch, cinnamon, and salt. (or you can just add your dry ingredients into the same bowl as your wet ingredients as shown in the video)
Slowly add the dry ingredients to the wet ingredients, mixing until just combined.
Chop up the semi sweet, and milk chocolate. You can use chocolate chips instead, if you'd like.
Fold in the chocolate chunks until evenly distributed throughout the dough.
This recipe does NOT require chill time; but chilling your dough in the refrigerator for at least 30 minutes will help prevent spreading and create a chewier texture. If you feel like your dough is a bit loose, refrigerating them will do just the trick to firm up your batter.
Using a cookie scoop or spoon, drop dough balls onto the prepared baking sheet. Make sure to leave enough space between each cookie to allow for spreading while baking.
Before baking a full batch of cookies, it's recommended to bake one cookie first. Place a cookie dough ball on the tray and bake for the full recommended time. The first batch of cookies may not bake the same as the following batches because the pan hasn't been in the oven. Alternatively, you can preheat the pan in the oven while the oven is preheating, but I prefer to bake one cookie first to ensure the batter is baking properly.
Bake the cookies for 12-14 minutes, or until the edges are golden brown and the center is set, but be careful not to over bake them. Even if they seem a bit underdone after 14 minutes, take them out of the oven as they will continue to set while they cool down.
Remove the cookies from the oven and allow them to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. Sprinkle them with flaky salt.