Slice the potatoes into ½cm slices.
Blanch the sliced leeks in boiling water for a minute and drain.
Butter a gratin dish, then layer the potatoes and leeks, seasoning with salt and pepper and a sprinkling of herbs between each layer.
Pour on the stock, just covering the potatoes and finish by sprinkling the cheddar over.
Cover with foil and bake in the oven. Check after 40 minutes and remove the foil to brown the top for 10 minutes.
You could opt for a locally produced cheese, like Winterdale Cheddar, which is wrapped in cotton muslin and matured in a cave dug into the chalky North Kent Downs