Heat oven to 190C/170C fan/gas 5. Prick the potatoes with a fork, rub with the oil, then toss with sea salt. Arrange on a baking sheet and bake for 1 hr. Let the potatoes cool for 10-15 mins, then cut a small cross in the top of each and pinch the bases to open a little. Add a teaspoon of soured cream to each, a little freshly ground black pepper, and a sprinkling of chives. Serve straightway.