Preheat oven to 400°F.

Wrap beets in double layers of foil and roast on a baking sheet in middle of oven until tender, 1 1/4 to 1 1/2 hours. Cool to warm in foil packages (the steam makes beets easier to peel), about 30 minutes.

While beets are roasting, cook onions in oil in a 12-inch heavy skillet, covered, over moderately low heat, stirring occasionally, until soft, about 20 minutes. Add salt, sugar, and vinegar and cook, uncovered, stirring occasionally, until onions are very tender and caramelized to deep brown, about 20 minutes more. Add wine and boil, stirring occasionally, until liquid is reduced to about 2 tablespoons, 3 to 5 minutes. Transfer mixture to a food processor and pulse to a coarse purée. Return to skillet and season with salt and pepper if desired reheat onion marmalade, covered, over low heat.  It is great at room temperature too.

Peel beets, discarding stems and root ends, and cut crosswise into 1/8-inch-thick slices with slicer.

Place the marmalade on a plate and spread in a very thin layer to cover bottom. Arrange beet slices in 1 layer over onion, overlapping them only enough to cover onions. Drizzle oil over top, season with pepper and sprinkle grated orange peel over top.

Works great the next day too.