SWEET POTATO FRIES WITH HARISSA MAYO

600g Evangeline Sweet Potatoes • 600ml vegetable oil or sunflower oil, for frying • ½ tbsp sumac • ½ tbsp fine salt • 1 tbsp rose harissa • 2 tbsp mayonnaise or vegan mayo • 1 unwaxed lime, zest of all, juice of 1/2, 1/2 in wdges to serve