Serves 4-5 as a snack

I've never really been sure what to do with these weird-looking French potatoes. They are called black truffle potatoes, blue congo or violetta, and they are blue all the way through. The English version are called salad blue. I've tried mashing them, but they turn a bizarre shade of mauve which people find off-putting in mashed potato. I've sliced them into salads, and you can boil them, but I couldn't resist turning them into crisps. Snack food can get away with being weird and wonderful, but they often charge an outrageous price for a few slices of crunchy potato, so if you can find the blue potatoes in the first place (try and farmers' markets, farm shops or direct from the Northumberland growers), make your own.

400g blue potatoes, washed
Vegetable or corn oil for deep frying
Fine sea salt

Slice the potatoes thinly with a mandolin or on the side of a grater. Wash in cold water and dry well on a clean tea towel or kitchen paper. Pre-heat about 8cm of oil to 160-180°C in a large thick-bottomed saucepan or electric deep-fat fryer. Fry the crisps a handful at a time, stirring every so often, then remove with a perforated spoon on to some kitchen paper. Season with fine sea salt, or you could use your own spice mixture, such as crushed chilli and salt or celery salt, or paprika and salt.