many thanks to those who helped, and apologies to Dr. Dawn, who got my first, and not so great batch. I cheated on the measurements in one respect, in that I found a non-metric measuring glass (one of those little shot glasses with teaspoons, millileters, and oz on them) that my Grandma had sent me. The first batch had dark brown sugar in them, which was terrible, but I used light brown for the second and it came out fine.
1064.7 ml flour
2 teaspoons baking soda
500 grams butter
354.9 grams white sugar
354.9 grams light brown sugar
a generous soup spoon of vanilla extract
3 bars of chocolate, one dark, one plain, one milk, chopped up
Lots of chopped walnuts
baked at 200 C
Took a little tinkering but these came out really well. I might add a little more flour and sugar to the next batch to see if I can make them a little more crumbly. This recipe makes very soft, moist cookies.