Scrub and wash potatoes very well using a vegetable brush. Dry with a paper towel and rub with olive oil; sprinkle generously with coarse sea salt.
Bake potatoes in oven for about an hour, or until fork tender. Allow potatoes to cool until they can be handled but are still hot; about 10 minutes.
Using a knife, cut an oblong hole in the top of the potato. (You may need a clean dish towel or mitts to handle the potatoes.) Using a spoon, scoop out as much of the potato pulp as you can, leaving the side walls intact. Scrape the pulp out of the tops you cut off, too, and discard the "lid".
Return the shells to the hot oven for another 10 minutes to crisp.
Meanwhile, mash the potato pulp using a potato masher, adding butter, salt and pepper, garlic, onion, cream, yogurt , cheddar (save a little cheese for the top) and chives. Taste and adjust seasonings.
Spoon the mixture into the potato shells until heaping full and return them to the oven. Sprinkle tops with remaining cheese and paprika.
Bake in 425°F oven (on top rack) until tops are golden and bubbly, about 10 minutes -