Quarter the potatoes (its optional but you can leave the skin on for extra flavour and texture) and par boil until soft enough to mash, without being fully cooked or too soft. Drain, set aside and leave to cool.
Chop the courgette into very small cubes. No more than a centimetre or so. Place in a large mixing bowl.
Add the onion, very finely sliced.
Add the herbs, egg and crumble in the feta cheese.
Using a masher or fork, loosely smash the potatoes into a coarse mash. It needs to be lumpy and don't worry about the odd 'chunk' of potato getting through. It adds texture and bite. Add the potatoes to the mixing bowl and mix in with the other ingredients.
Add the milk very slowly, a tiny drizzle at a time until the mixture feels soft enough to bind. If you add too much it will become sloppy and the fritters will fall apart during cooking so add just a drop at a time and keep testing until you feel you the right consistency. Try rolling some in your hands to see if it sticks together if necessary.
When you have the right consistency roll into tennis ball sized balls and flatten on to a baking sheet or chopping board in burger shapes. Covering the board in cling film first will stop the fritters sticking and make lifting them off easier.
Lay another sheet of cling film over the top of the fritters and seal the two sheets of cling film around the edges by squeezing them together. This stops ice crystals forming on the fritters when they go in the freezer.
To make sure the fritters bind well and don't fall apart during cooking its best to cook them from frozen so time allowing, place in the freezer for an hour before cooking. This isn't essential and they can be cooked from chilled if in a hurry but you will need to be extra careful and gentle when turning them over in the frying pan.
To cook, add some oil to a non stick frying pan and fry until each side is golden brown and they are cooked throughout.