Preheat the oven to 200ºC 

Rest the sweet potatoes in a large wooden spoon (to stop the knife cutting all the way through) and slice along the length of each sweet potato at regular intervals. Rinse and dry them then arrange on a baking tray and sprinkle over a few generous pinches of sea salt. Place in the oven for 45 minutes to an hour. 

In the meantime prepare your toppings. Grate the comte, squeeze half of the lime juice into the sour cream and add some salt and pepper, finely slice the jalapeno, spring onions and chives. Cut the remaining half lime into wedges to take to the table.  

Remove the sweet potatoes from the oven and grate over some of the comte so it melts. Take the tray to the table with the rest of the comte and a hand grater so people can add more as they wish along with the other toppings.