Heat oven to 360° F
Cream the butter and sugars until very light and fluffy, about 5 minutes
Add egg and vanilla, beating until incorporated
Add flour on a low speed until just mixed (dough will look crumbly)
Fold/stir in the chocolate chunks with a spatula
Put parchment paper or a silicon baking mat on baking sheet
Scoop cookies into 1 ½ T mounds, spacing them apart on the prepared baking sheet
Sprinkle each with a few flakes of sea salt
Bake for 11 to 12 minutes, until golden on the outside but still very gooey and soft inside
Rest on baking sheet out of the oven for 5 minutes
Transfer to a cooling rack