1. Steam the potatoes over boiling water until barely tender, about 5 minutes. Let the potatoes cool slightly on a plate.
2. Cut each potato in half and use a small melon baller to scoop out an indentation, leaving a 1/4-inch shell. Cut a thin slice from the bottom of each potato cup so it won't wobble.
3. Preheat the oven to 400° and line a large baking sheet with foil. In a bowl, toss the potatoes with the olive oil and season lightly with salt. Arrange the potatoes, scooped side down, on the baking sheet and bake in the lower third of the oven for about 25 minutes, or until the undersides are golden. Let cool slightly.
4. Arrange the potatoes on a platter, mound each with sour cream and top with caviar and chives. Serve immediately.