Cream butter and sugar(1 cup), add egg and vanilla and mix some more. Add flour(1.5 cups) and mix to a dough. Chop nearly the whole 200g bar of choc (i am usually left with two rows) into smallish pieces (it is about 1 cup) and add to the dough and mix in. If the board you cut the choc on has crumbs of choc add them too...they just melt into mixture when it cooks. 

Put heaped teaspoons full onto lined trays and bake at 190 degrees for 10-12mins.  Leave to cool for a minute or two before you completely cool on racks. Enjoy.