Preheat the oven to 350°F (180°C).
Add softened butter to the mixing bowl along with the white sugar and cream them together with an electric mixer until smooth.
Add the vanilla extract and egg and mix in.
Sift the all purpose flour into the mixing bowl and add baking soda, baking powder, cornstarch and salt. Mix in by hand (don't use your electric mixer for this part) into a thick cookie dough.
Add the milk and mix in.
Add the white chocolate chips or chunks and mix into the dough.
Break off pieces of the cookie dough and roll them into balls. Place them evenly on a parchment lined baking tray. Aim to get 20 large cookies from your cookie dough.
Bake in the oven for 12 minutes.
When the cookies come out of the oven, press more chocolate chips or chunks directly into the top of the cookies.
Leave them on the tray to cool down.