Preheat the oven to 350F.
In a bowl, whisk together the flour, baking soda and salt.
In a large mixing bowl, beat the very soft butter with the sugars and vanilla extract. Add the egg and beat until smooth. Add the flour mixture and stir until blended. The dough will be soft and sticky. Fold in the chocolate morsels.
Drop by tablespoonfuls on an ungreased cookie sheet (I like to line it with baking paper) about two inches apart to allow room for spreading. Bake for nine to 11 minutes (nine minutes for a chewy cookies; 11 minutes for crisp cookies) with the cookie sheet one the middle rack of the oven.
When the cookies are done, take out of the oven, leave to cool for two minutes on the sheet then transfer to a wire rack to cool some more. Leaving the newly baked cookies on the sheet to cool for two minutes help firm them up. Straight out of the oven, the cookies are still soft.
If you don’t believe me, try lifting (use a spatula or you’ll burn your hand) one cookie right after they come out of the oven. Do it again with another cookie after two minutes. Notice the difference.
Cooling on a wire rack prevents the cookies from turning soggy. Heat creates steam. The hot cookies still emit steam even after they have come out of the oven. The steam condenses, turns into moisture which gets trapped between the bottom of the cookie and the solid baking sheet. Ergo, soggy cookies. To prevent this from happening, allow air to circulate around the cookies freely so that instead of moisture getting trapped, it evaporates into the air.