Place the cashews in a large bowl and cover with water. Cover the bowl with cling film and leave to soak overnight or for at least 4 hrs.
Drain and rinse the cashews then add them to a food processor with the nutritional yeast, lemon juice, 1/2 tsp salt and 1 tbsp water. Whizz until very smooth, about 5 mins. You may need to stop and scrape the sides down with a spatula.
Transfer the cashew cheese to a dish or bowl and stir through the chives, if using. Cover with cling film and place in the fridge for 1 hr to firm up a little. The cheese will keep in the fridge for up to 3-4 days.