Melt the butter in a pan and cook onion and garlic for 5 minutes until soft. Put into a large bowl.
Add the ground nuts, breadcrumbs, lemon zest and juice, cheese, chestnuts and artichokes. Season with plenty of salt and pepper then mix in the egg. Stir in the chopped herbs. Preheat the oven to 200C/400F/gas mark 6.
Put the mixture on to a sheet of lightly buttered foil and shape into a fat sausage, packing it tightly. Wrap in the foil and leave to cool. (At this stage, the dish can be frozen until needed.)
Bake for 25 minutes (or 45 minutes from frozen), then unwrap slightly and cook for a further 15 minutes, or until golden brown.