Mustard greens, Swiss chard, or arugula can be used instead of or in addition to the spinach. These savory omelets can also be thinly sliced and served as hors doeuvres.
Melt 2 tablespoons butter in a large sautÃ© pan. Add onion, and cook until soft and translucent, about 8 minutes. Add spinach, one handful at a time, letting each wilt before adding more. When all spinach has been added, season generously with salt and pepper, and add the nutmeg. Remove from heat. Let stand until mixture is cool enough to handle. Squeeze moisture from spinach, and coarsely chop leaves. Set aside.
Whisk together 6 eggs and 1 tablespoon water in a medium bowl. Season with salt and pepper. Melt 1 tablespoon butter in a 12-inch nonstick sautÃ© pan over medium heat. Add the egg mixture; as eggs begin to set, push them toward the center of the pan with a rubber spatula, letting the uncooked part run underneath to fill the void.
When eggs are cooked but not yet completely dry, slide omelet onto a baking sheet. Crumble 1 1/2 ounces goat cheese along one long edge; cover with half the spinach filling. With your hands, carefully roll into a neat log. Using a large metal spatula, transfer omelet to a serving platter with the seam side down. Keep warm.
Repeat process with the remaining ingredients. Cut each log on the diagonal into individual pieces, and serve.