This is easiest to make in a food processor, although you can mix by hand if you prefer.
Mix the cheese, breadcrumbs and leek or spring onion in the processor.
Whisk the yolks, herbs, mustard and seasoning together.
Add to the breadcrumb and cheese mixture and whizz again in the food processor.
The mixture should be quite moist and come together easily in your hand but if not add another yolk or a touch of water.
Divide into 10-12 pieces and roll each into a sausage about 5 cm long.
You can make them ahead to this point and store in the fridge for up to a day.
Dip in egg white, roll in the extra breadcrumbs and fry until golden brown in hot oil or lard.
Serve with potatoes or, for a lighter meal, with perhaps some grilled tomato and a salad.
You may also like to fry a few rashers of bacon to serve on the side.
