Preheat oven to 175 degrees celsius.

Cream the softened butter with the sugar.

Beat in egg and vanilla extract.

Mix together flour, baking soda, and salt.

Combine dry ingredients with butter/sugar mixture and fold in the chopped chocolate.

Chill the dough for at least 1 hour.

Roll the dough into 1 inch balls and place on a greased baking sheet, 2 inches apart.

Bake for 10 minutes at 175 Celsius.

Remove from the oven and allow the cookies to cool for 10 minutes, before transferring them to a wire rack to cool completely.