Preheat oven to 425°F. Scrub potatoes, poke with a fork, rub with olive oil, and sprinkle with coarse salt. Bake directly on oven rack for 1 hour or until soft when gently squeezed.

While potatoes are baking, heat a little olive oil in a skillet over medium heat. Add sliced onions, season with salt and pepper, and cook slowly, stirring often, until caramelized and golden brown (about 25-30 minutes).

Once potatoes are done and slightly cooled, cut in half lengthwise. Scoop out the flesh into a bowl, leaving a thin shell.

Mash the potato flesh, then mix in sour cream and 1 cup of the shredded Gruyère cheese until smooth.

Fill each potato shell with the mashed mixture. Top with caramelized onions and the remaining ½ cup of cheese.

Place under the broiler until the cheese on top is melted and golden brown (about 2-3 minutes).

Garnish with chopped chives and serve warm.