Place butter, sugar, brown sugar, and salt in a large bowl and mix until fluffy (which takes about 2 minutes on high with an electric mixer).
Add egg and vanilla gradually until fully mixed in.
Set mixer to low and then gradually add flour to the mix.
Mix in the chocolate chips by hand.
Place covered into your refrigerator to chill for at least 4 hours.
Put oven racks in upper and lower thirds of oven and preheat oven to 375º F
Drop 2-tablespoon mounds of dough about 2 inches apart onto ungreased baking sheets.
Bake, switching position of sheets halfway through baking until golden brown (about 15 minutes total). Cool the cookies on sheets on racks for 5 minutes.