Melt the butter in a saucepan and once it has just melted, transfer to a separate bowl and keep it aside.
Sift the flour, baking soda and salt in a large bowl.
Once the butter has cooled down, pour it into the stand mixer bowl along with the caster sugar and brown sugar.
In a medium sized bowl, mix together the egg, egg yolk, milk and vanilla extract.
Add this mix bit by bit to the stand mixer bowl, over the butter and sugar mix, while whisking it.
Once all of the egg mixture is incorporated, you can slowly start adding the dry ingredients.
As all of the flour gets mixed in, you can finally add the chocolate chips to the dough, then take it out of the mixing bowl, wrap it in plastic and let it rest in the refrigerator for 1 hour.
After an hour, preheat the oven at 375 degrees Fahrenheit and line the baking tray with a silicon mat or parchment paper.
Scoop out the cookie dough onto the tray with the help of an ice cream scoop, making sure there is enough space between two cookies.
Bake the cookies in the oven preheated at 375 degrees Fahrenheit, for 15 minutes, making sure you rotate the tray halfway through the process.
Once the cookies are done baking, take them out of the oven and transfer them onto a cooling rack.
After the cookies have cooled down for 10 minutes, enjoy!