Preheat oven to 350°F (175°C). Microwave the butter for about 30 seconds to just barely melt it (half soft and half melted).
Beat the butter with the brown and white sugar/s until creamy and pale in colour and sugar has dissolved. Pour in the syrup, vanilla and the egg, and lightly beat until just mixed through.
Add the flour, baking soda, and salt, mixing until combined. If needed, add in one tablespoon of the 'extra' flour at a time until the dough is still soft but easy to handle and firm enough to form one large ball (the dough should not be dry. I only needed 3 tablespoons of the extra flour).
Fold in half of the chocolate chips with your hands.
Scoop out 18-20 balls and arrange them on a lined baking sheet with parchment paper. Press the remaining chocolate chips onto the tops of each cookie.
Bake for about 10-11 minutes. The cookies will look pale and puffed up, but should be golden around the edges. DO NOT OVER BAKE or your cookies will become hard once they have cooled.
Allow to cool on the baking sheet for about 30 minutes.